Twilight Princess or Metroid Prime 3? Which one should I get im looking for a long game to play

Twilight Princess is a far better game. Don't get me wrong, MP3 is a good game, but it doesn't compare in my opinion. Also, the multiplayer isn't really worth anything in that game.

As for length, Twilight Princess took me ~70 hours to fully beat. I haven't fully completed MP3, but MP1 and 2 took me about 20 hours each (100% completion).