I have the geissman, the ATI super actinic and the fiji purple one. i am using a combo of the first 2 for supplements. The last one is way to purple/red for my taste but might be very nice if you had more the 2 running or if you were using them for other then supplementation. I got all mine through reefgeek.
Having use both ATi and Giesemann "blue" bulbs, I'd say without a doubt the ATi... ok maybe there's a little doubt, but from what others have said the ATi lasts longer, and is stronger output.
If you want 54watters get them from Ed, local and no shipping
However that being said he doesn't carry the 39 watt bulbs last I checked.
I've suggested to a few local guys to carry ATI bulbs, I for one would be buying a few, alas it seems that Hagen is the only company pushing T5HOs to LFS and I'm not too thrilled with the quality of their T5 stuff.
On my son's tank I went with 2 ATI aqua blues and 1 ATI blue plus with a ge 6500 along with a t8 actinic just because and I am sad to say his tank looks better than mine
I like the Blue+ bulb because it's light output is like 85% of the "white" bulb which is crazy since most bluer bulbs take a nose dive in output. This allows you to go with a more whiter halide, which in turn will have more light output. Plus I really like the look of a whiter tank when it's at "full brightness" if I want bluer look with the fluorescing colors when the halides go off the T5s are still on and I get that.