Good points David Rex,
The Derby is a very unpredictable crap shoot. Sure, Bellamy could go gate to wire, or he could get left standing in the stall like Holy Bull. X,Y & Z could get great or horrible trips, etc., etc., etc.
I say look at a few horses you really fancy
(5 or so with a top already capable of winning or, less likely, a great forging pattern plus the likelihood of a good pace and trip scenario) and put a small wager on the highest price. Most years you lose, but this approach works for me every few years or so [Thunder Gulch (25-1), Charismatic (15-1), Go for Gin (9-1), Unbridled (10-1)]. You can\'t make a living this way, but you\'ll keep you\'re shirt!