4X24w T5's without a doubt! I've had a 250w MH (14k, 10K, & 20K) on my 20g and when I put my T5 fixture it looked so awesome I promised mysef I would never go back to MH. The T5's make the colors explode on the rics and basically the unit emits no extra heat over the tank like the MH.
MH Setup
TEK T5 Setup
Rics Under T5's