My favorite is Lemmy.
The tribal war paint thingy is cool, too.
As for his picture in the manual, I thought that it was silly. But because of that silly pose, it somehow made me admire him more than the rest. Then again, I was a kid back then. Silly stuff grabs your attention.
But because of it, Lemmy remains my favorite.
I do share the opinion that the Koopa Kids may never come back, but some recent developments cause me to think otherwise. In any case, the Koopa Kids will come back for at least one more round, since there have been rumors of a SMB3 for Game Boy Advance.
However, the chances of Nintendo bringing back the Koopa Kids seem unlikely. Even although they did remember to bring the classic Zelda theme to Zelda Majora's Mask. It's like the other things we've seen. SOM2 was a good game in Japan, yet it never made way to the US. Fara was a good character in the Star Fox comics, and we'll likely never see her in any upcoming Star Fox games.
You can still see the Koopa Kids in all their glory though. There's some good websites, like Lemmy's Land, and there's even a site that includes downloads of the original cartoons. So they're still around in the world of today. In shadow, perhaps, but they're waiting for their chance to once again hit the big time.
May Yoshi live long and prosper...
Oh, and may PenguinWizard have the same treatment.