I chose A-Rod, first of all he is closer to Bonds than anyone else in the poll. He's almost to 500 and he is only 31, 32. Obviously an easy answer for now. Sosa and Thomas are too old and it'll take them another more seasons and will they want to keep on playing off their old, worn out bodies?
Pujols have the ability to catch up, however he is not hitting any much HRs like he should this season. Howard and Fielder are young so I don't know if they are consistent doing so. If they do, then fine, they can.