I like my 70w I run a 14k ushio, it works great for my 10g qt/zoa tank. I've had Acros and Montis under w/o a prob, they even grow pretty good too.
AFA 150w vs. 175w I think there are a lot of variables, one being bulb life. A 175w on an e ballast is going to last you a lot longer than a 150w on a "HQI". However, in most cases the 150w will be brighter, it will also consume as much if not more watts than the 175. Too many gosh darn variables..