But Lyle Overbay might be the most important of them all.
Yes, the other three have better offensive numbers. But Hafner doesn't play the field, Youkilis is on the disabled list, and the Yankees have more options in the outfield.
Overbay, as manager Joe Girardi admitted on Friday, is the only first baseman on the roster right now.
The 36-year-old signed a minor-league deal with the Yankees at the very end of spring training, just a few hours after being released by the Red Sox. Yet he's started 23 of the Yankees' 28 games thus far.
He's batting .239, with four homers and 12 RBIs. And he's committed just one error in 26 games in the field. Not bad for a guy who played only 65 games last season combined for the Diamondbacks and Braves, and was cut again in late March.
Mark Teixeira is making progress -- in fact, he's headed to Tampa on Sunday to continue his rehab, and expects to be taking live batting practice in the next couple of days.
But there's no need to rush. Last season, Teixeira hit .251, with 24 homers and 84 RBIs.
Over a full season, Overbay is currently projected to have 23 homers and 69 RBIs.
Teixiera is better, no doubt. But thanks to Lyle Overbay, the Yanks have hardly missed a beat.
ON DECK: It's a quick turnaround -- after a night game on Friday, the Yankees and A's play Saturday at 1:05 p.m. Phil Hughes (0-2, 4.67) will be on the mound for New York, opposed by former Yankee Bartolo Colon (3-0, 3.38). Yours truly will again be on hand, covering for ESPNNewYork.com.
QUESTION OF THE DAY: Which new Yankee has been the most important thus far this season?