So I thought it was worth getting total value (offense + fielding, approach initially justified here) estimates of player performance as a starting point. To hone down a list of players, I looked at posts by Andy at Baseball Reference's Stat 'o the Day blog, and by Pizza Cutter at StatSpeak. I also threw in a few folks that I thought were deserving of consideration who hadn't otherwise come up. Here they are:
Based on these data, I think it's probably safest to conclude that we should restrict ourselves to talking about a 5-man race between Wright, Pujols, Utley, Jones, and Holliday, as there's a 13-run dropoff between Holliday and the next closest player.
Pujols and Jones are on teams that are out of contention now, even though both teams were "in it" in early September. But since neither is clearly head and shoulders above the rest, this puts these two individuals at a slight disadvantage in my book.
So at this point, I'd put it as a battle between Wright, Holliday, and Utley. Holliday's fielding numbers are good, but Wright and Utley are the top defensive players at their respective positions according to THT's fielding data. Utley missed a substantial amount of playing time this season, and I think durability should be a factor with this award...though his numbers when present have been spectacular enough to rank him among these three despite the missed time. Wright leads all three in Win Probability Added, indicating that he's had a greater impact on ballgames this season than the other two (not that this is completely his doing). And, of course, Wright also led all of these players in my total player value estimate.
It's a tough call, but with a week left in the season, I'd probably give the award to David Wright.