I grow in 2 closets and have one off site closet. I use a 120w in one, a 300w in another and a 400w HPS Hortilux on the off site. I love my LEDs. Yeild wise I get more than my 400W HPS, my 120 is about the same yeild as my HPS. before any of this though I started with four 4foot T5s for flowering in a 2 X 4 closet. In my personal experience, all are great choices, it depends on what you want as a final result.
My T5s would yeild me about 1.5oz a month on a perpetual harvest (1/2 closet in each month, 1/2 closet out each month) I loved it. for me as a personal stash 1.5 Oz a month wasn't bad. The T5s work great for a SOG short plants about 8" high max before the T5s were crap. 8 smal plants in a 2 X 2 closet (half the 2 x 4) was really good. No heating issues just used a cheap inline fan venting out. Potency was good, plants very healthy, just couldn't penetrate more than 8".
The 400W was next. Huge improvement over the T5s (obviously) Took lots of venting (got a 5" inline fan to cool the closet on this one) Everyone knows what HPS lights do, they work good, but a lot of heat issues if you aren't careful. This was at my off site garden.
Then I bought a 300W LED and they gave me a free 120w LED for buying the 300W. Hooked up the 300w in the closet and put the 120w for veg. The 120 was to close to my vegging plants and bleached them. Very easy to do with LED. The 300w replaced my T5s and the T5s expanded my cloning/Vegging area. After first grow I had to scrap the 300w because I don't care what they say, LEDs make heat (a lot more than T5s) and I had heating issues and got a shit crop. So my 120W became the flowing light of choice. That worked great, minimal venting controls heat and no more heating issues, very little heat. 120w works great but I only grow either a few small plants under it or one big one. I use this closet more for breeding than anything else. The 300w works great I use it for in my 3x3 closet and grow 4 plants at a time under it. The 300w definately needs some good cooling, but works good when set up right.
I find the LEDs garbage for veg compared to the T5s, but that could just be the brand I bought. Overall I'm extemelly happy with my purchase, but it is a big investment. I love to try the latest and greatest gear and it's not always a good thing, but in this case I'm happy.
Happy growing everyone