I will offer my opinion here - I have used retracts in my warbirds - mainly mustangs - for over 15 years. I have tried mechanicals and air retracts and have found that the air up/spring down are the easiest to install and keep working. But you need to use a quality brand of retracts. If you go for the cheapest ones you can find you will live with problems.
So for your mustang type retracts (non rotating) I use Spring Air brand retracts. I use a Robart fill valve because this fill valve works easiest with the air compressor I use for them. I use oleos with them - an oleo is a spring loaded gear leg. I do not use wire gear legs, but if I did I would use 3/16 wires, not the smaller 5/32 wires, and I would be sure to get wires made from music type wire, which flex but do not take a set/bend on hard landings.
But the oleos handle the shock of a hard landing better than wire gear legs. So I use retracts that are made to accept the oleo directly into the retract without needing to grind short lengths of wire to go between the retract and the oleo - this is much simpler to adjust and stronger.
Most of my planes are 60 size mustangs. For those I use Spring Air (
www.retracts.com) 700 series 85 degree retracts with 7/16 Robart oleos, and similar oleos that are sturdy. I recently bought a set of Robart air up/spring down 700 series retracts which look strong but I haven't flown them yet. I NEVER have air leaks with Spring Air retracts - for the 10 plus years I have used them.
I have a couple of giant scale mustangs also, and I have used the same type of retracts (air up/spring down Spring Air 400 series) in one of those giant scale mustangs. For the other I bought Robart 622-5 air up/down retracts - but only because the air up/spring down retracts are not available that fit the Top Flite giant scale mustang directly.
I will look for pictures of my retracts, but if I get the chance I will take a couple of pictures of some that are not installed.
I avoid mechanicals because the ones I tried were hard to set up properly and when you include the cost of the retract servo they were about the same cost as the air up/spring down retracts. In addition to my knowledge the only mechanical retracts available that will carry oleos are the ones Hangar 9 uses on their planes and those don't have the offset oleos that the mustang uses.
Recently there have been lot of retracts advertised made in China and I haven't tried many of them. This is because the Spring Air retracts have been flawless and I don't see much reason to mess with them. I suppose if I found a set that I could look over before buying them I might try them if they looked like a good design, but the part that you can't see from looking is the type of aluminum that they are made from and how good the seal design is. So at this time I will stick to Spring Air and maybe Robart.
For rotating retracts Robinaire and Sierra seem to make good quality retracts. Rotating retracts are used on planes I don't fly so I don't have anything more to say about them.
Ed