If it's all about length, then put the Toy Cannon on the list. He'd belong there just as much as Allen.
But if the question is "Is there a player who, in his prime, would cause you to drop everything just to watch him take an at bat?" - Gotta say that my preferences will lean towards the guys who were not only sluggers, but great all around hitters.
Pujols, Howard, Mantle, Mays, Griffey, Aaron: these guys were great all around hitters.
Reggie, Strawberry, McGuire, Allen: these guys were all one dimensional sluggers for the most part.
Bonds? Lord knows what he would have been without the chemical assistance.
*new* Alex Jackson - Welcome aboard, AJaxx!
2014 Hitting .400/.458/.500/.958 in Peoria. Sure, it's only 5 games, but I think he's ready for A ball.
Forrest Snow - Back from suspension. Has jumped from Peoria to Jackson to Tacoma.
2014 AAA/AA: 1-2, 2.73 ERA, 25 K, 5 BB, 1.177 WHIP - more to come!
2013 AAA/AA: 5-5, 2.96 ERA, 84 K, 28 BB, 1.085 WHIP
2012 AAA/AA: 5-9, 6.35 ERA, 99K, 67 BB, 1.674 WHIP
Gone But Not Forgotten (former adopt-a-players):
Eric Thames - Hitting .332/.417/.648/1.065 in Korea (290 plate appearances).
Matt Mangini - Out of baseball. Assistant coach for a high school.
Mike Morse - Hitting .277/.331/.502/.833 for the Giants. (sure would look good as our DH about now)
Jamal Strong - Let go after 2005. Played in the Yankees, Cubs and Braves systems. Now a regional scout for the Cards.