I always have to pick Ocarina of Time, but it's because of sentimental reasons. It's my favorite game because of the stuff that was going on when I first got it and how awesome it was to me. Is it the "best" game? Probably not. GTA V is a pretty damn good game. Probably the best on that list, as far as 'good games' go, but I still have to vote for Ocarina
This is tough. Zelda & Skyrim are my 2 favourites. I'll probably say Skyrim as it had a lot more hours of game play. However Zelda was my favourite growing up. I still love playing Ocarina of Time even today.