There was a time when I used to think of vanilla as an insipid, plain flavor; I was always a chocolate guy growing up, like most kids. But, I have to say that while it's not my favorite, when you get a good ice cream with a rich vanilla flavor it's great by its own merits—without toppings. Still, I do enjoy adorning vanilla ice cream with hot fudge and the like from time to time.
It's hard to go wrong with chocolate, but in a way, plain chocolate ice cream on its own gets dull very quickly. If placed on a cone it'll gain some personality, but my favorite thing to do with it is to make a chocolate malt with it.
Chocolate and vanilla swirl soft serve results in a very satisfying amalgam.
Mint chocolate chip was one of my favorites, too, but I think I've kind of grown out of it. Maybe it's just because I kept getting the Dreyer's brand, which I actually hate for its airy texture; I have a predilection for heavier, richer ice creams.
Rocky road is great in its complexity in both flavor and mouth texture, and I really enjoy nuts in my chocolate. One of my main gripes with it, however, is that its embellishments mean it isn't the best candidate for a milkshake.
But, if I had to select a single type of ice cream I would go with coffee ice cream. Trader Joe's has a fantastic coffee ice cream that's one of the best I've ever had. I can't think of anything better, so I'd have to say that it's my current favorite.