Wing shape has never been an issue for me. I started with DSS Horseshoe wings and moved into HOG donut style. What counts more from my observations as I've also tried Dive Rite and Hollis wings is technique and proper weighting. I have an article I can send you on BPW systems that I've sent to dozens of people all over the world. It answers many of your questions. Short version answers are as follows with a little detail.
1. Wing shape does not seen to matter as much as your ability to manage the air in the wing. I've had no issues venting from horseshoe or donut wings. Mainly due to not needing to add amounts of air that present management problems. When you are over weighted you need to add excess air at depth to compensate for that. This becomes problematic as you go shallower since that air is expanding. If you happen to be horizontal and elect to use the inflator to dump, you may not get it high enough to vent as much air as you need. Newer divers to BPW's may get a little flustered and end up going up too fast and blame it on the wing. It's not the wing. It's diver error from the weight standpoint coupled with poor technique. IF you use the lower dump people tend to pull it straight out or down to vent. You really need to pull it up towards your arm pit to get the best results. If however you have excess air in the wing I've seen people pull up on the cord correctly but instead of staying horizontal they start to get a bit head up and allow the air to move to the top of the wing. Therefore they don't get effective results, again, from poor technique.
It is true that donut wings will allow somewhat better air flow throughout the wing. I exclusively use donuts now.
Lift is the perhaps the most important factor in a wing. Too small and it won't give you sufficient lift for the plate, your tank, the regs you use, any extra gear, etc.. I have been taken to task for some of my recommendations on wing lift and the considerations I take into account in them. But for me and my students I stand by them.
A wing needs to float your gear at the surface. It needs to allow you keep your chin out of the water. I also believe it needs to provide sufficient lift to assist another diver in the most likely scenario you may encounter. The last is where people don't always agree with me. But having been involved in a number of diver assists I stand by it.
I sell wings (HOG and Manta) starting at 23 lbs of lift on up. I rarely recommend the 23 to new divers. Unless they are only going to be diving an al 80 tank or similar with an aluminum plate in tropical conditions where they require little or no weight. For anyone who is going to be diving a steel plate, steel tanks, in cooler or colder water, and in an area where they are likely to encounter other new divers the minimum I recommend is the one with 32 lbs of lift. I had a 23 myself for travel but did not see the benefit between it and the 32 as far as size and compactness were concerned. I also did not see any increased drag from the larger wing. Underwater I'm not concerned about speed so drag is really a non issue.
I have been involved in some diver assists and was glad I had that extra 9 lbs or so of lift. Especially when dealing with an over weighted diver who was having problems staying afloat.
There are no junk wings from any of the main players in the BPW field. One thing to note is that HOG wings do have a ten year warranty against pinch flats thanks to the ballistic material used for the bladder.
As for the STA, some wings require you to use an STA. Either due to the fact that they don't have slots for tank straps or lack another method of controlling the roll of the tank on the plate. Others use blocks or rods to accomplish this that are attached to the wing. For some STA's are convenient. For me they are not. I swap tanks a lot and use different plates. My freedom contour plate won't accommodate an STA.
STA's can help to lower the amount of lead needed on the belt. They do move the tank higher off your back and raise your center of gravity. One person I did sell a package to with an STA said for the first few dives it felt like he was more unstable than without it due to the higher center of gravity. The larger the tank the more this was felt by him. He got used to it but mostly only uses the STA for specific dives.
I have never used an STA on a regular basis as the set up on the HOG wings just doesn't require it.
I've owned over the years somewhere in the area of 8 BPW sets. Right now I only have four. I've sold dozens and shipped them to customers all over the world as kits they put together and assembled so they only need to make the final adjustments. I'm pretty good at setting them up with a few personal details so that the adjustment step is usually quick and painless. What I have found is that no one has ever felt that my wing lift recommendations were off base. Several who first thought they needed no more than 23 were glad they got the 32 when a situation came up where the extra lift was needed.
Ideally we should be properly weighted and so should everyone in the water. We all know that's not the case. There are still instructors out there that don't have a clue producing divers who lack one as well and are diving seriously over loaded with lead. My dive buddies usually aren't. But then it's not my dive buddies I may have to assist. It may be one of those clueless divers or instructors and I want to be ready. My personal opinion again but one that has worked in real situations.
I'd be happy to send you the article if you send me an email address as well as perhaps help you with a purchase of your own set up.
