For me, there are too many inconsistencies in Zimmerman's story to believe his version of events.
As a guy that's seen a few fights and even been in a couple myself, I've seen people sustain far worse injuries than his... His injuries don't make sense in light of the life threatening struggle he describes. Zimmerman has no defensive wounds. How is that? Does that mean he just laid there and took it when he thought his life was endangered? That doesn't make sense.
At no point did Zimmerman identify himself or his purpose in following the guy, and claims he didn't do so because he was scared. However... shortly thereafter he's out of the car following the kid he's so scared of. Why? If he was so concerned for his safety one second, why did he feel safe the next? In one version of events Zimmerman says the kid RAN away. In another he says he SKIPPED. Even if you ignore the ridiculousness of that statement, what it means is that he doesn't consistently describe the speed at which the kid was going, which is important because if he wasn't going fast it means that they were in the same place at the same time for a minute and a half or more.
One of the witnesses described a prolonged verbal confrontation before the fight. It's almost entirely absent in zimmerman's version of events... (His version goes like- Trayvon: Do you have a ******* problem? Zimmerman: No. Trayvon: well you do now! *starts pummeling*)
Anyway, I think it likely that things didnt happen as Zimmerman described because I can't trust his story, it just doesn't make sense to me. However, based on the evidence, he'll either be found not guilty or, if he is determined to be guilty, it'll be of the lesser charge. If he is found guilty, it'll likely hinge on the fact that he followed the kid without identifying himself, and created a volatile situation either knowingly or unknowingly in the process.