I run both the Albins S5 and the Fortin FRS6 in class 1 (although I'd not run the 6 in the US, the 5 has wider gears).
I'll give my 2c. The Albins has required very little work. I'm wearing the side plates on the Torsen. Only because I race short course in my desert cars and using the cutting brake works the torsen hard.
The Albins "feels" more solid in shift. It's a solid shunt between gears and the dogs "grab" to each gear. It's very hard to select a false neutral, in fact it's very hard to select "neutral" which is half a detent between 1st and 2nd, like a motorcycle pattern.
The Fortin has had it's first season and we'll pull it down after the next race. It's not as solid in shift and you have to be a little more forceful with it. When I'm tired I tend to select more false neutrals. Which I'd guess happens every 2-3 hours of racing. It has a better shift pattern than the Albins, having both neutral and reverse through the reverse lockout.
I think one thing that you should not only consider the strength of the box, but support. All the boxes you have mentioned will require regular rebuilds and parts. I don't know about Albins support in the US, however Doug Fortin was fantastic with the build, expert advice, custom gearsets, for the FRS6 when it was states serviced. Just ensure you can get great support for whatever box you select.
For me, being remote, I'd go Albins, Fortin, then a distant Mende. The Mende might have altered since it was bought by Weddel, however the reliability here (pre Weddel boxes) hasn't been the greatest.
100% agree with Weddle/Albins combo. Always fast service, easy to get a hold of, honest, and to the point. We had a couple little issues when first got our Albins but Weddle took care of them and since then trans has been flawless in the past 30k miles with only a couple rebuilds just for preventive maintenance. 1 time went 13k miles and thats when the clutch finally broke. Apparently Centerforce doesnt recommend that many miles. Our car is a big 4 seater with 550hp, 37s, and weighs 4600lbs.