I am not voting because you did not put Yellow, Crystal or Emerald in the poll, which were my favourite Pokemon games of all time.
HOWEVER-
While Crystal had the whole "Let's go to Kanto again!" thing after the Elite Four, it was kinda crap. I mean, we only got some gimped versions of the cities, and the whole map took about a fifth of the time to complete than the Johto one. Emerald, on the other hand, gave us the Battle Frontier, and for that, it gains my vote, even if you couldn't get all three starters in it (With Crystal, you could get the starters through a glitch of changing boxes).
Edit: I do have a qualm with the series as a whole in general. Most of the rare (and hence, best/most fun to play with) pokemon were found post-Elite Four, and by then all you really wanted to do was either a) Go to the Battle Frontier with your trained Pokemon, or b) Start a new game. Thankfully, Platinum rectifies this (as well as the whole absence of starters thing) with the Global Trading System. So I vote Platinum. Oh wait, you didn't include that either. T__T