Hi, nbkoc,
Garry Dallas, one of the top SM instructors strongly advised me into the
Diamond system. I've not tried other, but Diamond serves me really well. It has EU certificate, too. Just take care to equip it with the
sliding rings (rigid D-rings with slightly bent base) on the waist belt for trimming the tanks and consider a continuous loop, as it comes with two separate loops.
Apeks SM regulator set is hard to surpass. But the most important for starting side mount diving is to find a really good instructor. Why don't you try
Garry? He might be willing to go to your place to give you a tutorship.
https://www.facebook.com/Simplysidemount?fref=ts
Oh, yes, if you opt for Diamond system, I warmly recommend to get also the
weighting system. Without it, the weights are threaded on you waist belt and make the rig permanently heavy. The DTD produce it and they were so kind to make for me one with the pockets opening away from centre and with additional
inner pouches so that you can pull out the weights. Originally it is designed for cave diving where no one would consider ditching the weights. I think, now this modified model is on their product list, too.