If those are the only 2 options, I would say HPS. I have not used a mars hydro but my skepticism toward them being good for growing is huge. On Amazon they list a coverage of 1.5x1.5 for bloom....so for 8sq feet you'd want at least 3....and then you're pulling just as much juice as 400w HPS (mars hydro is listed @ 132watts actual).
I would suggest LED but you're going to want something better. COB lights seem to be doing great things. Personally I went with the Growmau5 kit from cutter electronics for my 2x4 tent. The Amare shown above looks awesome as well!