Need imput about white boxes

I am setting up a small nonfor profit company with 20 computers. No name brand computers, they were burnt by one two years ago. So I have a set amount to spend on hardware. My question is what is the best main board around? Least problems, easyest to work with, good tech. support and upgradable at low to mid cost? I have done a ton of research of alot of them but it more then one sided. I would like imput from the people who work with them all the time.