Doing a lab type comparison would be difficult IMO. You could do a single 150W MH compared to 3 - 54W T5HO tubes but the results will not mean much. The halide would likely give higher numbers directly under it but the T5's would give usable par over a much wider space. So this comparison would not help much.
I think the only fair comparison is on use by use basis. Setups such as a 65G (36"x18"x25") vs (48"x18"x24") vs (72"x24"x29") are all going to have much different results.
Lets take my tank for instance. 4'x2'x2'. If I intended on using dual 400W MH's, then no other lighting system I know of will produce equivalent par. MH wins game over. However, that is much more light than I would want over my tank, too much heat, too much electricity used, probably cook most corals. So, I would be looking at some dual 250W MH setup. I like fluorescent supplementation so I have to factor that into the cost and additional par. Several options here, but the light I ended up getting is a dual 250W HQI (14K) with electronic ballast and dual T5HO Actinics.
The challenger is an ATI Powermodule. This light has active cooling, true T5 spec ballast, and individual reflectors. You can get it in 4, 6, 8, and 10 bulb setups. I think the 8 bulb is what I would opt for over the 120G. I would use some combination of 10K, 15K, blue +, pure actinic, and procolor bulbs.
Of these 2 setups, I figure both would easily handle SPS up top and probably toward the middle of the tank. Both should give nice color but I would say the Powermodule would do a little nicer just based upon the number of bulb combinations. The halide would give the shimmer which is nice. Par, well I would love to know the difference. I think it would be very close with the ATI giving a much more even spread throughout the tank but I have no facts to back that up. The ATI would produce less heat and use less energy just based upon the 176W less electricity used.