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.
Alex Jackson - Don't hold your breath. He appears to be going backwards.
2015 Clinton/Everett: .207/.318/.365/.683
2014 Peoria: .280/.344/.476/.820
Forrest Snow - Pitched decently in Tacoma, but couldn't even get a Sept call-up. No cups of coffee in the doghouse.
2015 AAA: 10-9, 4.17 ERA, 96 K, 41 BB, 1.31 WHIP, 121 IP
Career: 28-40, 4.36 ERA, 533 K, 219 BB, 1.30 WHIP, 586 IP
Gone But Not Forgotten (former adopt-a-players):
Eric Thames - A star player in Korea, hitting .381/.497/.790/1.288 in 2015 for the NC Dinos.
Matt Mangini - Out of baseball. Assistant coach for a high school team.
Mike Morse - Bad year in his good year / bad year cycle: .231/.313/.336/.649 for the Marlins and Pirates
Jamal Strong - Let go after 2005. Played in the Yankees, Cubs and Braves systems.Last seen as a scout for the Cards.