I am going to echo some of the same things HSA said.
I grew my first crop of 3 plants under a 4 bulb t5 setup. I didn't have a lot of knowledge, so the plants stretched on me, but I still ended up with around 1oz off each plant, and it smells and smokes amazing. I recently picked up a couple 3ft plants from another grower who has a 4000w hps grow. Yes, his buds were MUCH harder than mine, and larger in size. He included some samples of finished meds with the plants, and frankly, the bigger harder buds still have a very green, hay like odor to them after 2 weeks curing in the same fashion I am curing mine, and mine have a very pungent, bud smell.
I passed a little of my harvest along to a more experienced smoker, and the feedback I got was that he was amazed at how smooth it smoked, and the awesome flavor, even out of a pipe.
I just upgraded to an 8 bulb t5 fixture, and moved my 4 bulb to my veg area. I am currently using 4 "blue" bulbs and 4 "red" bulbs in the 8 bulb fixture.
So for yield, I would echo what everyone else is saying, go MH/HPS if you can deal with the heat. If you are patient, and are growing for personal use rather than donating to a club, t5's seem to be an excellent choice, when coupled with some sort of training of the plant to maximize your limited light. Keep your plants short, wide, and well topped and you will have a great canopy to harvest.