Haven't decided yet between soft pack and straight harness and backplate, but here's what I am considering. Any thoughts?
When I moved (from a Zeagle Ranger) to BP/W, I tried a Halcyon set-up, and tried a Transplate. I ultimately went with a used Dive Rite SS BP, bought some webbing and set up a one piece harness myself, with buckle, D-rings, etc. So, my comments on your possibilities should be interpreted in the context of my personal bias, toward simplicity, which may or may not be yours. I also later bought a used OMS backplate that came with a Deluxe Harness (not the Comfort Harness, but with a chest strap, quick releases on both shoulder straps, etc.) that gave me a broader experience with 'gizmo gear'.
Of the harness and backplate systems you mention, I might look at the Transplate as the simplest approach, although even then it is more complicated than you need for single, or future back-mount double, tank diving. I don't find a chest strap to be useful, for singles or doubles. I don't find shoulder padding to be useful for either (unless you are a CA shore diver, or a FL springs diver, and enjoy hiking to the dive entry carrying your gear
). I DO like having a quick release, but only on one side, and only when diving doubles and a drysuit. Otherwise, the quick releases are not very useful for wet, single tank diving. Your consideration of the Renegade suggest you are looking for a weight system other than a standard weight belt, though, and that may be a factor in YOUR decision-making. The OMS Comfort Harness is too much 'stuff'. Personally, since it worked for me, I recommend a simple SS backplate, a one piece harness, and some D-rings, as the easiest way to make the transition to BP. I prefer a STA when diving singles, but that is just me. I would also stay away from Soft Pack systems, in general, with one possible caveat, that I will come back to. The OMS IQ Backpak is, from my perspective a no-no - not very adjustable, too much unnecessary material. If you think that a plain vanilla BP with a single piece of web harness is too austere, then the Renegade or Transplate might be good for you.
My caveat may not be Herk Man's 'bait ball in the shark tank', but some might consider it a 'turd in the puchbowl' comment. And, I appreciate your initial comment, that there are so-o-o many options, that it is already confusing. But, having recently gone over to the darker corner of the darkside - sidemount - I have a somewhat greater affinity for the TransPac than before. It still has way too much padding (I took all of it off my unit when I bought it for SM), but it does allow you to start with a rig that will accomodate a single tank, and move with reasonable ease to two tanks, with the addition of a buttplate and some bungees. The problem I am having is that there is such an explosion of SM rigs, it is hard to say that the TransPac is better than (or even as good as) some others. For example, in looking at the Oxycheq Recon SM rig (since you mention looking at the Renegade), it appears that a diver could use that for a single back tank. For someone who is seriously considering moving to tec in the future (two tank diving is 'tec' to many) you may want to explore the option of a SM rig. Just a thought, although maybe a premature thought. (And, just as Ulysses had the Sirens to lure his ships onto the rocks, I suggest you go to
www.gosidemount.com/videos.asp, and click on video, Demo in a Razor Harness.)
We are currently finishing a class of tec students, all of whom are doing it backmount. It may be one of our last BM tec classes, as I want to try and move people toward SM in the future. In fact, this afternoon I am taking a diver, who I just certified last summer in OW, to the pool to have him try out my TransPac Nomad rig, to start moving him to two tank diving.
Since 'tec' is a future, not present, consideration, it may be easiest to just look at a BP/W now. But, I thought I would throw the SM thought into the [-]punchbowl[/-] er, mix.