Valley's & Dufferins to start. The ones with the the most even points are good ones also. They'll save you some unnecessary work and be a better cue for it. The better the cue to start with, the better the end result.
They can be warped in the shaft area, just make sure that the handle is straight. You may wind-up making a lot of shafts.
If they measure out at .840/.850" @ 28-29" from the butt, so much the better. You'll have plenty of meat to work with and to adjust things.
You can get by with less if you have to but if you've got a choice, why would you want to?