They're completely different. SteemPeak is very much about looks, but it's a pretty hefty site. It uses way more ram than a lot of other sites. Steeve is more minimalist, and still very much a beta site. There is a very useful feature below most posts that gives you other blogs to "Read Next" though. That is the primary advantage.

I like SteemPeak for it's grid view and wide margins. Though that can be a disadvantage when someone posts something you don't wanna see full screen. :P But I've found myself using Steeve to find posts because of that "Read Next" feature. I think it needs a lot more work though.