From my limited knowledge of this case and what I understand, Manslaughter would be appropriate. Murder? Please.
If the jury believes Zimmerman was defending himself than manslaughter is not even appropriate. The wrong of profiling and following Martin doesn't eliminate Zimmerman's deadly force self-defense when (if) Martin jumped him.
Manslaughter is when you recklessly kill someone. Am I to believe that pulling out a gun and shooting someone when you are getting your head bashed in, or when the attacker is reaching for the gun themselves, is reckless? If you are saying that Zimmerman was getting his head smashed in, but is still guilty of manslaughter, you are saying under the law that it is reckless to shoot someone when you are in fear of serious injury. But I don't believe that's reckless, I believe that's justified.
IMO People want to convict Zimmerman for wrongfully setting in motion a chain of events that led to Martin's death, but which Martin himself had a hand in acting wrongfully. They want the "reckless" part to be how Zimmerman was following and profiling Martin, but all that is cut off from the second that Martin jumps him (if he did indeed do that).
Now, the jury can do whatever they damn well please, they don't have to explain how they arrived at their decision. They can convict Zimmerman of manslaughter to "punish" him for following Martin even if they believe Zimmerman's story that he was in fear of his life. The jury doesn't have to explain their actions. But if they followed the law, and they believe Zimmerman's story, he would be acquitted of both charges.
It depends on what you believe happened. I haven't heard any evidence that leads me to believe Zimmerman threw the first punch, or that he was on top in the struggle. All the other stuff is completely irrelevant when it comes to the murder or manslaughter charge.
The Prosecution's argument has been that, Zimmerman is lying. Zimmerman threw the first punch and Zimmerman was on top, it was Martin that was crying out for help.
Their argument for those things, though, has been pretty well disproven. See the original post in this article, there is just no way that Zimmerman was on top.
So if he gets convicted, it's because the jury wants to punish him for following Martin. Which would be wrong to convict him for.