The choice is really up to you and what you think is going to work best for your corals.
The actinics are on a different wavelength than the halides, usually between 420nm - 460nm. These provide the blue coloration that not only simulates dawn to dusk, but also makes the corals flouresce. These work very well if you are using a "whiter" metal
halide bulb, such as a 10,000K.
Metal Halides come in different Kelvin (K) ratings which let you know how much of the blue light spectrum they give off. 6500K is a little yellow, 10,000K is crisp white, 14,000K is slightly blue, and 20,000K is very blue. There are also variations in between. Each of these K ratings gives off a different level of PAR as well, with 10K being the highest and 20K being a little lower. It basically comes down to preference.
Most of the fixtures that you are describing come with 10K halides and actinic supplementation. You could in theory run just the halides at say 14K and possibly get good results as well. This would allow you to save some electricity as the PC ballasts would not be running. However, since they are power compacts the savings may be negligible.
I have been running my fixture with 10K halides and actinics. I am seriously considering switching to 12K and still running my actinics for just a little more blue coloration in the system.
Many people run halides only without actinics while others would not have a tank without actinics. In the end it is up to you and what your preferences are and what you feel gives your system the best results.
Is that long winded enough for a non-answer?
