Galaxy makes a *very* nice 150w electronic ballast. It runs both MH and HPS. It's completely silent also, which is big plus for me. They make a regular 150 and a dual 150 that will drive two bulbs, so if you check prices, make sure you're looking at the single.
It's a tough call as far as 150 versus 250 heat-wise. I've done back-to-back comparisons, both with remote ballasts outside the grow area, and the 250 got about five degrees higher Fahrenheit to give you some idea.
A 150w electronic ballast does provide about 20% more lumens than magnetic coil ballasts, so the light output is pretty good for a small personal grow.
I don't recommend you get one of the lights that are all-in-one because having the ballast inside the grow area will make it significantly hotter.
I have a Galaxy 150w and Lumatek 250w electronic ballasts, and love both of them. I actually just recently bought another Galaxy 150w on ebay cause it was too good a deal to pass up.