I would consider some dimensional stable wood species,such as Burmese teak, domestic Walnut, Santos Mahogany, etc. Staying in 2-1/4" boards helps. I don't think the 3" will perform much difference with the more stable wood. Quality engineered wood floorings should be considered if stability is the main concern.

Quarter sawn wood move in thickness mostly.

Thank you UniqueWoodFloor and brickeyee, we're going to pick out flooring tomorrow, hopefully, so we'll bring these suggestions with us and see what they have - and what we can afford.

Quarter sawn hardwood will expand and contract approx 1/2 as much as flat sawn wood. You will have to ask a dealer but most won't know what you are talking about. LL for sure! I would suggest purchasing Charles Peterson's book Wood Flooring by Charles Peterson I obtained it at amazon.com. about $30 you will get it in a few days. Most important thing is proper moisture content of wood and subfloor if not you can have real problems.