I have all, Apple TV, Roku, and Samsung smart TV....
I'm an electronic junky. I say Roku is the best if you had to get one. The apps are better, and you get BYUtv on it. Apple TV is easier to use then Roku/Samsung, but I'm dissappointed with then since they started streaming them from your desktop and took away the option to store them on the appletv device (them = movies/etc). Samsung I think is the worst of the products (same with Vudu for those inclinde to buy a Vudu device).
My advice though, if you have apple computers stay with appletv, if you don't, then its a preference. Roku is nice but they essentially do the same thing!