ORIGINAL: Silversurfer
First, go with a 50cc plus, not a 45cc. More aircraft options later.
Second, there are a lot of great engines out there in this size range. It will come down to fitting your budget. Fox, First Place, Brison, BME, 3W, Taurus are a quick few I can think of, and not necessarily in that order.
Third, that "burbal" you hear about is directly controlled by the needle settings input by the user, and the stage of break in the engine is at.
I agree! Some good advice from Silversurfer. RE: His third point...For every complaint I read about the DA... usually twenty or so guys wrote in and said theirs were awesome. I think the user was a factor, or perhaps the break-in was not that far along.
I think DA and Taurus will tell you the wait is about 3 or 4 weeks.