I've used giesemann and ATI. I prefer ATI, because of the par I get from the blue plus and the color spectrum of the coral+ bulbs, a great blend of colors I use:
Front to back
Blue+
Blue+
Purple+
Coral+
Blue+
Blue+
ATI here as well.
Blue+
Blue+
Blue+
Coral+
Blue+
Blue+
Honestly you could probably get away with all Blue+ as they actually provide somewhat of a white-ish coloration with all 6 bulbs going. Just my experience though. The great thing about T5 is you can tinker with your spectrum (for $20-30 a piece though).