For a read-only (one way databinding) databound control, they are the same (I'm guessing Bind has slightly more overhead since it has more functionality, but I can't confirm that).
For 2 way databinding (using a datasource in which you want to update, insert, etc with declarative databinding), you'll need to use #Bind.
Simple as that. Eval is read only, Bind allows for data to go two ways.
Why dont do a simple google search?
eval bind difference:
http://www.google.co.in/search?q=eval+bind+difference&rls=com.microsoft:en-us&ie=UTF-8&oe=UTF-8&startIndex=&startPage=1&redir_esc=&ei=RKutTNzTK4yCvgOi-uT0Bg[
^]