All depends on budget and preferences. .. some may swear by halides, others t5 and others may say leds. I personally use leds a few reasons I choose leds ,cost efficient great colors not as hot as halides and others .don't have to change bulbs out in leds.so to me I weighed out the costs and I use leds. Radion g4 I believe are pretty popular.it kind of also depends on what u want to spend also
I personally run but t5s and leds on my 36 and everything is awesome. From what ive learned t5 is for growth and led is for looks if you are on a budget like me. Obviously they have leds that can grow but they are so expensive. Im running a coral life fixture and a kessil tuna blue.