I'm sure a lot of people are going to say Leader Brawl. But you know, he's such an insignificant character in the movie compared to everyone else. I know, Brawl's a great Leader class toy, with lights, with machine gun, and grenade-launching sound effects. Interesting transformation, and so on and so forth.
But there are drawbacks to him too. Like the annoying clear parts, annoying sound effects, and the top 2 turrests that keep falling off. His main gun just hangs to the side, whereas the Deluxe, he can actually aim it, which is cool. Leader Brawl also has really skinny arms. I mean puny. If you like tanks, then hey, go for him.
Megatron. I chose to get Leader Megatron simply because he is Primes nemesis. The Leader of the Decepticons. His robot mode is actually pretty neat. His alt mode gets a lot of negative remarks because it isn't an earth alt mode. But remember, Megatron didn't give a rats behind of anything earth. He loathed the planet, and the pests infesting it. So, why would he take on an earth mode?
That said, his alt form is still kind of weird. You can see his head, and his colors are wrong. Well, okay. But it is original.
I have to admit, I had a REALLY hard time deciding between the two. And frankly, I feel your pain here. I wish I could be of better help.
Brawl beats Megatron in almost every catagory. But Megs is the still the badass leader, and he is the tallest, and widest of the three Leader figures so far. Even though he isn't as flashy as Brawl, he is still a pretty decent toy.
It comes down to what you like, and what you want. If you would rather have the leader of the Decepticons, and don't mind Megatrons quirks, then there you go. If you don't care, and just want a kickass tank, then there is Leader Brawl.
I chose Megatron because Brawl is dead, for one, didn't play a significant role in the movie, is dumber than a bag of hammers (read his stats and bio), and his sounds seem to be annoying. Plus I wanted a Megatron since I only have ever owned 1 Megatron in my life. That being Titanium WWI Megatron. GI Joe Titanium Megatron has been demoted to canon fodder fake Megatron.