Roadtrash:
You will want a blade that covers your tracks when it is angled to throw dirt/gravel/snow to one side or the other. I have a 6 foot blade with my 25 HP Ford 1520 and it handles it well. At times, I would like to have a 7 ft blade. Kind of depends on how much maneuvering room you have where you will be using it. Do you need to get between narrow obstacles? You can always raise it a little to take less of a bite if what you are blading gets too heavy.
Brand is really personal preference. Mine happens to be a Ford brand, but has minimal adjustments (angle or reverse only). It does what I need to do, however/w3tcompact/icons/smile.gif. Some allow tilt adjustments at the blade, rather than just using the tilt adjustment on your 3-pt hitch. Others have full hydraulics to adjust blade angle, tilt, etc. Some also allow offsetting the blade to reach out to the side a ways. Just depends on how much you want to spend and whether you have remote hydraulics available. My closest implement dealer happens to handle Leinbach equipment, which I find to be heavily built at reasonable prices.