[Crazy Jetty]

I can't say I know anything about Megablock minifigs, but I think given the fact Hasbro launched Kreo with TFs, the kreons are likely the most adaptible of all.
However, Lego has so many decades behind them, they have the most customizable accessories for their minifigures.
Waspinator is, to date, the only kreon I have. And it's so close to being a great, but Kreo's lack of intuitive accessories totally botches it.

Anyway... Lego minifigures are great for simple humans like Harry Potter, Indianna Jones, and Luke Skywalker. But they sometimes tend to halfass other things, and I could have easily seen the turtles ending up being halfassed with only painted details (instead of having a removable shell and new heads), like the Kraang. For that reason, I'd wanted to see Kreo get the lisence originally. I'd thought Kreos would have likely been more willing to alter their "iconic base figure."

All that said, I think that the UK's Character Builder has the best minifigures. Anyone who;s never heard of them, google Character Builder Doctor Who.
There's actual sculpting going on.