Hi,
If you are planning on having a halide only pendant, i would recommend a DE (double end) halide setup. Get some more light, smaller pendant size and more dependable bulbs usually. SE works fine too though.
IN the 20K DE, it's a personal preference. I think the 20K AB bulb looks the best compared to XM and Coralvue. Then the 14K Aquaconnect looks as blue as the 20K AB but more intense. The Hamilton 14K i think looks nice, because it's just a little blue, not too much. THe 20K Geissman should be nice too, but i've not used one before.
If you go SE, your choices are limited in the 20K, have Radium or XM. Radium is brighter and more blue, but XM is a good value and has shown good results with corals. There is a 14K aquaconnect SE and a 14K hamilton available in SE. There is a 13K Geissman but it's not blue at all, more like a 10K.
Hope this helps.
thanks