DEpends on how you are going to use it.
Reader has more functionality that Foxit but Foxit is a smaller application than Reader. They both seem to function pretty well but I would say that Reader has more users (but that's simply a guess. There's no data available to prove either way)
There's no way any of us can tell you what's better for your use.
The one thing that counts for me is that Adobe Reader does not install spyware on my system!
If you are looking for an alternate PDF viewer, you better look for something different than Foxit!