*Looks up where Caldwin is in relation to the rest of the show*
Well, you're almost halfway done. Just a little more until it actually starts to get interesting.
As for my favorite versions of all the cast:
Leonardo: Hmm...this one's tough, because he's usually the most "bland" or "responsible" out of everyone. I think I might go with 2003, because he does have a hidden rage underneath his usual stoicism in this version. IDW's pretty close, with his dark-side arc, but...I just have more nostalgia attached to the 2003 version.
Raphael: IDW for me. He's arguably the "heart" of the team in this version. He the one on his own in the beginning and reconnects with the family later. He has the best relationship outside the team with Alopex (...we'll see how the current storyarc plays out). He fights as a vigilante/cop for Mutant Town. I think he's the most layered version of himself, here.
Donatello: 2012, I guess. I'll admit, 2003 comes pretty close, too. But, 2012 just came across as more "human". His crush on April can be awkward, but some of his reactions to some of the situations they find themselves in can be fun.
Michelangelo: 2012. This just feels like the most "Mikey" Mikey we've ever gotten. Upbeat. Childlike. Optimistic. He still gets a "idiot savant" power, like the 2003 version, only this time in Dimension X, which feels more deserved since Mikey just goes with the flow more, which helps in a alien environment.
Splinter: Again, 2012. He's just fun. His lessons are sometimes contradictory...and he admits that. He kind of feels like he's still figuring out the whole "master" thing, and that's kind of unique. Although, no spoilers, but Rise probably changes the most over the course of the show. Despite the rocky start, Rise Splinter IS a contender, believe it or not. IDW might actually be my LEAST favorite Splinter, since he kind of loses his way a little after taking over the Foot Clan.
Casey: 2003, no contest. He's still the voice I hear in my head when I read Casey in comics nowadays. He's probably one of the better fighters. But, not a complete psycho.
April: It's close, but I'm going with IDW April. She has the best combination of "usefulness" and "fitting into the plot". The 2012 verison has more power...but she honestly became a little "Deus Ex Machina"-y to me. 2012 April almost became TOO important to the plot, if that makes any sense. 2003 has a great relationship with Casey, and probably has my favorite personality and voice of all the Aprils, but she doesn't get a lot to do. IDW April is a scientist, which is useful to have around. Although...if "Shredder's Revenge" April counts...she might be a contender.
Krang: Um....2012. As overused as they are, the Krang actually get a interesting origin, even if it does feel like a retcon.
Shredder: 2003, no contest. I don't care if he is a Utrom, or a Tengu, or a Cybernetic construct. This is the Shredder I judge all others by. His voice and leitmotif are iconic. He's actually threatening. It's ALWAYS exciting when he shows up. For the record, the Utrom Shredder is specifically my favorite, but ALL the versions of him are pretty good. IDW Shredder comes closest to recapturing a lot of 2003's cool, but...well, him being someone else's pawn kind of waters him down in my eyes.
