I'#ve never hear the Q150, but as it's got less power than the Q200 I've not be too keen to get one, if I were you.
I've just got a Servo 15 and I also have a Storm III. I guess not being married has it's advantages... Anyway, I tested the Q200 and Storm and found easily in favour of the Storm - goes lower (easily to 18Hz when positioned in a corner) and louder.
However, the Servo 15 goes substantially louder than the Storm III and it also goes lower. I don't think it's as musical as the Storm, but I've not completely made up my mind on that one yet.
Oh, you'll never hid the Servo. It requires more than twice the floor space of the Storm, but is not as tall. Oh, it weighs 41kg in it's akward size box - and I put my hip out carrying it up three flights of steps!
Cheers,
Rob.