As a die-hard Trekker... of the two, it's almost a toss-up.
Troi is definitely hotter, even with the slightly lopsided boobs... but Crusher is easier. Look how often Troi got laid (and how!) in 7 years, and what did Crusher have... Captain Picard occassional panting heavy for her?
Besides, as of Star Trek 9: I Think I'm A Clone Now, Troi is married and off the market.