in my opinion the best and cheapest is Bansko sports, I know you dont get the liift discount like Ulens, but they are cheaper so it works out the same and they open at 08.00 so you can ski early. The staff are very helpfull too.
it is near he gondola. from town you turn left at the top traffic lights (near the gondola) and they are about 50 metres down the road in a tent. There is a short cut opposite straight to tthe gondola.