Jesse Plemons would make a better lead for Star Wars, Episode VII, because he has naturally blonde hair and he just looks right for the part. He also has a lot of exposure already, because he is a star in Friday Night Lights. I would like to see him have his big break.
Frankly, I'd never heard of any of these actors, but I looked them up online and I'm going with Ed Speleers. He's acted in Eragon, a fantasy film not unlike Star Wars. Plemons, on the other hand, seems to have concentrated on contemporary characters in gritty shows like Breaking Bad, roles unlike the sort of characters you'd see in a Star Wars movie.
Given his work on Breaking Bad in particular and the intensity he showed in that role, it is possible that Jesse Plemons might make a good lead. However, Ed Speelers has proven on Downton Abbey that he can act well and be sympathetic. Therefore, Speelers seems like a better choice for the lead in 'Star Wars: Episode VII' than Plemons.
In my opinion, neither man deserves the role. At one time, it was rumored that a black actor was being considered for the lead which would be a fresh take on the "Star Wars" saga. With the exceptions of Billy Dee Williams and Samuel L. Jackson, most characters in George Lucas' six-movie saga are white. Jesse Plemons is probably the more recognizable of the two men. Plemons and Ed Speleers look like Obi-Wan Kenobi or maybe even a son of Luke Skywalker with their blonde hair. However, I think J.J. Abrams should go more diverse this time around and make his "Star Wars" protagonists more like the bridge of the U.S.S. Enterprise with a diverse cast.