Well, I saw one of the (if not THE) Galaxy's fastest players, Brian Mullan, in full stride just get run past by Landon Donovan. I'd say Donovan is the fastest man in MLS. It was scary how he flew past Mullan.
I think Ray Hudson could outrun Sigi. Wheras Bob Bradley would just beat their asses and walk across the line. I'm not gonna say he's the fastest, but it seems Milton Reyes can catch anyone.
My first thought was Beasley but after reading all these answers, I realize we'd have a pretty good competition with 10 or so players in a good ol' fashioned 100 yard dash. My money'd be on Donovan or Herdsman.
Valderrama? Considering that few of us have ever seen him actually run, we may not ever know how fast he is.
I've never seen him in an open sprint, but from what I have seen, he didn't look al that fast. Put my money on Run DMB.
I don't necessarily know if he's the fastest but, oh my God is Donovan fast! And on top of that, he's still ripping up the field in the 88th minute when everyone else is exhausted!