LED = low power cost
LED = low heat,
so no need for additional cooling or fans = saves more power cost
LED = a little more expensive than HPS,
...but remember - if you get the HPS you probably need a cool-tube, larger extraction fan and possibly even an air conditioner in the summer
The Piggy has you taken care of man, BS240 is PERFECT for 2x2. Make sure it's not more than 2x2 and throw a couple CFLs in to supplement.
Here's the thread he recommended, check it out for some beautiful BlackStar shots.