I really think these two guys are really close.
Bay, 28 yrs. old
105.5 runs, 33.5 HRs, 105 RBIs, 16 SB's, 944.5 OPS
106 runs, 34 HRs, 102 RBIs, 12 SBs, 931 OPS
Holliday, 27 yrs. old
(1.5 year averages)
101.5 runs, 32 HRs, 121 RBIs, 13 SBs, 949 OPS
104 runs, 28 HRs, 99 RBIs, 13 SBs, 941 OPS
I think your draft day decision comes down to a few things:
1) Categories - I'd take Holliday in a batting average league, and I'd probably take Bay in an OPS league, because of the number of times he walks.
2) Speed - Do you believe in Bay's stolen base numbers in '05 or '06? Personally, I think that he'll run a little more in 2007 than he did last year, but it may not be enough to turn the corner.
3) Protection - If Bay hits 5th for the Pirates, then he won't really benefit from the LaRoche acquisition. If LaRoche hits behind him though, I think a bump in stats is going to be the result.
4) Coin flip - Not to cop out, but these guys should probably be drafted back to back, unless you really have a gut feeling one way or the other.