You got a lot of really good advice in here, vakiter. I mostly love boosting on a twintip, but also spend a good bit of time foiling. I've got Flites in 12 and 17 and Prodigy 9.5 and 7. Actually, I just bought a Crave 9, so there's that, too.
The Flites are a little lighter and seek the edge of the window a little easier, which I like for foiling. The Prodigy is a little better at drift, but seems a smidge heavier (I've never weighed them, so that's strictly my gut feeling). The Flites are really responsive, so being active with them can sort of compensate for lack of drift. I've only managed to foil the Crave once (this was a 12m), but it seems to have fairly similar drift to the Prodigy. More time will tell, but that's what I've observed so far. And for what it's worth, I think that GregK has it spot on; that Aluula Roam will fit the bill for both foiling AND boosting. We had guys here at our demo that were getting some stupidly good loops on the 10m while other people were riding 12's and 14's. Pretty good for a "surf" kite.