OK, after thinking about this for a while, here’s my list (based on the TCs only), and coincidentally its’ divided in three groups of three:
Strong characters
Tygra: I think there was a lot to him (just that the producers didn’t show us). Everybody sees him as a shy, dull guy, but I think he was the “think before you speak” kind of guy, considering every aspect of a situation before jumping into conclussions. His character is kind of controversial and contradictory as well: he was appointed as the second in command (and it seemed to me the other TCs saw him that way), but he was the one left out of the action the most times. It’s like he was a loner most of the time, maybe he thought/felt his mates don’t get him.
Yes, he was shy (as he himselff confessed) and didn’t need to call for attention. But he also had to struggle with an addictive personality (maybe due to that same shyness) and his moral concerning his mind powers. Also, I think he felt overshadowed by Pantrho’s personality, and all he had was his knowledge, but when Lynx-O came into scene, he even lost that (that’s the only thing I didn’t like about Lynx-O, he took the “wise” role out from Tygra), so he looked refugee in his introversion.
On the other hand, he was really mature and level headed, but all that fell when confronted with his personal issues. He also held the code the best between the TCs. He apologized when he got it wrong (Garden of Delights, Mossland Monster) or when he got the others in trouble because of him, and always thanked thems when they had to save him (Turgamar the Tuska, Mossland Monster, Fireballs of Plun-Darr, Out of Sight)… I never saw any of the others doing that, as if they took it for granted that the team was there for them, Tygra didn’t, and that showed his maturity and integity.
Finally, even though he wasn’t the main charatcer in most eps (and he was the one written off the most), the eps he was in as the main character were some of the best on the serioes.
Cheetara: Another strong character, very dual as well. She was wise and prudent, even getting annoyed at the others, especially Lion-O, for rushing into action and letting pride domintate them. She was also the one who scolded Lion-O the most, while Tygra tried to be comprehensive about Lion-O’s “child in an adult body conidtion” and Panthro just seeming eager to be his friend and forgiving him for everything. She was also rude and aggressive when her firends were in danger (she confronted Safari Joe while she was in the cage, for example)
But she lacked of self-confidence as well when it came to her sixth sense. She didn’t trust herself, so she didn’t think her friends will… she first thought his friends will consider her crazy when dreaming about Wiz-Ra, tehn was afraid of failing and the others not trusting her anymore in Telepathy Beam; nevertheless, she recovered from it and conquered her fears, taking her power to its maximum potential.
To me, it was no coincidence that she bonded that much with Tygra: both of them had a strange, powerful ability that drained them, and that they didn’t know how to handle it very well. They both lacked of self-confidence some times (maybe because of their powers too), and they both seemed to be worried about Lion-O’s growth and maturity (at least more than Pantrho showed to be). I would have loved to see an episode where they both (Cheetara and Tygra) would have been forced to use their powers in order to save the day.
Wilikit: Yes, this might be surprising. I think that, from the two, Wilikit was the strongest when it comes to personality. She not only teased her brother, but showed to be more “everything”: wiser, more prudent, braver, more sensitive. Whil Wilykat looked for fun and adventure, Wilykit kept her feet in the ground (maybe because feminism was a raising m,ovement back in the 80s?)
She also displayed better battle skills, and had this rolling-over-her-hair thing that I liked.
Middle caharcters
Lynx-O: it ws good to introduce this character, the only one of the new TCs that was worthy IMO (maybe Pumyra for being the other female TC, but only because of that).
I liked the idea of an old, wise character, that was also blind! But they could have worked with this more… Lynx-O seemed to have assumed his blindness very well, and felt confident of himslef, which is a good thing, but they could have shown his frustration and/or fear at his condition sometimes. I liked his light shield too (it could have been bigger though).
The only bummer for me is that he seemed to know almost everything, especially in season 2… I think it was because of the introduction of this character that both Tygra and Jaga made aside in the writers’ minds.
Lion-O: ok, so being the lord and main character, we’ve got to get some in-depth into his character, knowing him the most.
I liked Lion-O insecureness in the beginning of the show, not in the “brave” term, but in how to act or react because he was still a child’s mind… I would have made it a little longer though, seeing his maturity as a process, and not form one episode to the other. But I liked that we got to learn about his fears, pain and nostalgia concerning his home palnet; we saw him living the greif process the most, and that was good because he had so many things to process.
He was a good leader overall, compassive and caring for his friends to teh point of willing to sacrifice himself for them, he kind of learned how to be judgemental and take good decissions, and he was brave. The Demolisher episode was one of his grown-up points to me: instead of battling him and destroying him, he called his freinds to prevent him of doing so, giving Demolisher a chance.
On the other hand, Lion-O had still a long way to go when the series ended. He was impulsive (he controlled that a bit through the show), and think he should do everything ebcause he was the leader and had the sword, sometimes dimishing his TC mates abilities. And of course, I didn’t like that, by the end of the series, he solved everything with the sword.
Wilykat: I liked him, really, and maybe because of that I don’t place him among the “weak characters”. He was fun, but he was also really immature, always wanting just to be part of the action and complaining about not being able to do so. He used to be the one who talked Wilykit into trouble (while she was usually the one to talk him out of them), and between the two of them, he got caught the most.
I liked his outfit 
Weak characters
Pumyra: I feel bad for putting her in this category (kind of considered putting her in the middle one), but let’s face it, she was lame, plain and almost useless. Her character had potential as the group’s healer though, but besides that, they didnt’ give her any speacial ability (she was the most agile… after the kittens, the fastest… after Cheetara, so it seemed she was kind of the second best in everything, but never the most in something). They also forgot about her healing abilities, and sent her to the background.
I didn’t like her design either: she looked like a regualr woman with a lodge’s hat, a wig or a very bad hairdo.
Finally, her weapon: if they wanted her to have pellets, she could have had ones like the thunderkittens; I never got what was that kind of whip for (was it supposed to be a kind of slingshot?). I knew that with the introduction od the new TCs, writers could have had trouble bringing on new weapons (the weapons seemed to be very lame: a shield -which I actually liked, but it was no that useful, the slingshot, and a hammer?)
Pantrho: I already said this, and still think that way. He tried to be rude, but to me, he came accross as Archie’s Moose Mason, talking rude and threatening, but with no brains at all. I never liked his sense of humor either (to me he has none, but he was supposed to have it), and it was like he tried really hard to become Lion-O’s BFF, bnever correcting him and looking for the chance to spend thime with him (when Tygra or Cheetara would have been abetter choice given their life experiences and ages).
Also, it’s the TC we got to learn the least about… maybe he tried to come out as a funny, bully person to hide his insecurity (which would have been nice), but as never saw a hint of that, I don’t know. The eps that centered around him (I think it was only Split Image) were boring, his trial was boring, and he was the one who resembled a cat the least lol. Oh, and the bat phobia was too far-fetched IMO.
If Pantro was written off, I wouldn’t have missed him.
Liked the nunchucks though.
Bengali: he is tthe one I have the biggest problems with. His character was almost a mixture of all the others. He was a watered version of the kittens+Tygra+Pantrho IMO.
He brought nothing new and did othing at all but bad jokes, complain and steal show time from the others. I think if they had introduced only two new TCs, it would have been better becasue they could have developed Pumyra’s character more, and not send Tygra to the background. Pumyra and Lynx-O would have been enough.
Also, in “Thundercats Ho!”, whenever the new thunderians were about to get free (on themselves), somthing happened to/with Bengali that frustrated their attempts, so he was the weak link of the trio IMO.
They could have done something with him. For example, given his desing and blue colors, he would have made a good spy at night.
His weapon was also lame IMO.
Point taken, though. I rarely run into anyone who really remembers TCats, and even less that would still watch it now.