From what I have found, it seems as though O and B-Type stars are the hottest types in our galaxy. O-Type stars range from 30,000-60,000K and B-Type range from 10,000-30,000K. I know that O-Type Stars evolve much quicker than others because their temperature and pressure is more favorable to hydrogen fusion, which is what, essentially, causes stars to form. There is a really good description of this at this website from the University of Georgia: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/procyc.html#c1
Hope this helps!!