I completed the gen 5 pokedex quite easily although I have not come close to finishing the 6th gen one. I generally wait until the 3rd version of the game so I can trade between the two. So I will finish it when Z comes out eventually.
I can't remember, but I know my Pokedex is incomplete (as in I've seen many Pokemon, but some of them still remain unseen). I've never been able to complete a Pokedex until Gen 6 (still need 3-4 more entries, but close enough). lol