Can I suggest you buy the best regs that you can from the outset? Get a set that you can dive in any conditions and that will remain of use to you if you decide to progress your diving.
I bought a Scubapro MK25/S600 to dive single tanks when I first started about six years ago. By the power of fleabay and YD personal ads I now own three MK25's, two S600s and a couple of R390s which are serving me very well on my twin 12s and stage.
I can't coment on Apeks, but my buddy Eeyore uses them and they seem popular with YD folk, as do Poseidons, of which I have no personal knowledge.
Good luck with your purchases and have fun finding them
Helen xxx