I would highly recommend the PFO 250watt Dual 65K Metal Halide Retro Kit from
Premium Aquatics. Since your AGA is 24 inches deep I would recomend a dual 250watt set (MHs are effective over a 2'x2' area). With 250's you can keep anything from mushrooms to SPS. If you are planning on keeping clams, go with a dual 400watt set.
As for color, go with 6500K bulbs. Make sure to get this model of bulb MT250DL E-39/41R 6500K. The R in there stands for reef. 6500 is on the yellow side, but when it is combined with
VHO Actinics the color blend is very pleasing to look at.
I know it is a fiancial hit, but I would buy the VHOs and the MH kit at the same time. A LN Electronic 2 Bulb VHO Kit sells for $129. I would recomend getting two
URI VHO 48in - 110 watt Actinic Blues.