I have owned a couple different apeks regs and currently use a XTX 200 with the FSR first stage. I love it, in fact over the weekend I had in water that was 42f at 60ft and as usual flawless performance. That being said you could save some money by going with the XTX 100. I can not find any difference in the two except the finish on the first stage. Also look into HOG regs, I have never tried them, but have heard nothing but good things about them. As for the SP regs a lot of guys like them, I have never used one so I can't give a opinion on them. Good luck, and let the debate begin.
Have fun and be safe.