ORIGINAL: Julian537
I once read that the two surfaces vs 3 had one less place for the prop vortices to get caught on and wash off. This was less drag. Sail planes also use this configuration for the same reasons that MJD stated. less joints for induced drag and tips.
Basically you get 2 of some of the bad things instead of 3, with the net gain being on the good side. As to the prop vortices, if the total area is maintained between equivalent V and cruciform tails, I don't kin the difference, but maybe there is one.
Another critical factor not noted here yet, is that to many people, V-tails look really cool.
BTW Walkers210 - I strongly suggest that you search this AND the Q500 forum to see all the beef-up and set-up tips that are highly recommended for that aircraft - if you haven't already done that already of course. It is supposed to be a good flier and last for more than one flight, if you make a few simple mods.
MJD