I think there's a real difference between cold-water and warm-water optimized rigs. Likewise, the difference in demand between recreational and technical sidemount adds a lot of factors for consideration. Any rig will suffice the average non-technical/overhead sidemount diver; but the more demands your diving creates, the more you need a special-to-purpose rig.
If you will be frequently travelling, primarily using ali cylinders, diving wetsuit/warm-water...or going into restricted overheads, then I don't think you can beat the 'British' approach sidemount rigs; such as the Razor or Stealth. Minimalism is the key factor.
If you want something more heavyweight, with larger capacity and more weight options, for use with drysuit and/or steel cylinders; then the 'US' type rigs are hard to beat. I think the SMS75, Halcyon and Nomad lead the field.
I've got 5 rigs at the moment; ranging from super-minimalist (DR Trim Pillow on DIY harness) to very heavy-weight (OMS profile with Custom Divers Dual-Bladder TDB). Both of those rigs have specific purposes. For all-round diving, I use an
Aquamundo sidemount - it's basically a Z-Trim copy, with some changes, made locally in the Philippines. That does fine for 2-4 Al cylinders and moderate tech or overhead.
I've recently been using a
SubLevel rig, that was sent to me for trial. I really like the bladder design on that... but had to minimalise the harness to my own needs/specifications. It has dual-bladder option, so it fills my need (agency standards) for buoyancy/redundancy when I am teaching TecRec courses. I'm told they're doing some similar adaptations for a new tech-focused model at the moment.
---------- Post added July 3rd, 2014 at 08:35 PM ----------
I just noticed this new review on the Halcyon sidemount online:
Scuba Tech Diving Centre, Cyprus: Halcyon Contour Sidemount System- A review