I'm also using XM 10k's on magnetic ballasts. They are very bright, and the color is pretty nice with supplementation. I went with the XM's because of the insane amount of PAR, since I knew I would be starting this tank with mostly frags and I want good growth. After the tank grows out and I'm not as concerned with the growth, I will probably switch to a 14k or 20k bulb for the nicer color, and maybe an HQI ballast so the PAR doesn't drop off too drastically.
I agree that it would be best to get a DE setup if you are buying new, but don't overlook SE because you can usually find some good deals on used systems. If you do go with DE, be sure to buy HQI ballasts - electronic ballasts don't drive DE bulbs to their full potential, so you lose the benefit of going DE in the first place.