Well, from personal experience, I vegged under warm white cfls then flowered under an HPS, and it worked just fine. If you only have to pick one light, I'd go with the HPS. HPS works fine for veg (shit, mine grew like a weed under it), and it is by far the better spectrum for flowering, so if you only had one light to use for the whole process, you'd be better off with HPS.

We were just discussing something similar in this thread, scroll down to see the pics I posted a few posts down. http://boards.cannabis.com/showthread.php?t=95140

So, from experience, light intensity is more important than light spectrum. Go with the HPS, you will not be disappointed. The main difference is the blue spectrum causes slightly shorter, denser plants during the veg cycle than the red spectrum, but not to the point where its a big deal IMO.