I'd buy a 400W HPS system because I feel it gives you more options. You can buy a nice HPS bulb with an enhanced spectrum for flowering and get a MH-conversion bulb for vegging.

I'm not sure about the chrome vs. white reflector so hopefully someone else will drop in. Though, I like the idea of not using a reflector and just using mylar but I'm not sure how well that would work in your space.