You know that players no longer get to choose their HOF hats -- thanks to Wade Boggs.
When Boggs was negotiating with the Tampa Bay Devil (at the time) Rays near the end of his career, he tried to use the HOF hat a a bargaining tool ... in return for more money, he offered to pick Tampa Bay for his HOF bust.
The HOF quickly stepped in and assumed responsibility for picking hats.
As for Sheffield, I think it would be Marlins -- not only was he there longest, but it was in his prime and that's where he won his one world championship ring.
For Vlad, as of this moment, he's played 1004 games with the Expos and just over 800 for the Angels. He won his only MVP with the Angels, but finished ranked in the MVP vote more often with the Expos. Tough call, but since the point was to talk about "drop dead" HOFers, if he was being voted on based on today's career, I'd say Expos.
But another couple of years in LA would change that.