There's only three makers of transfer-bar equipped SAs.
Throw the Taurus Gaucho out of the running. QA issues.
The Beretta "Stampede" series is similar in size and heft to the Colt SAA, which means it tops out at 357. You can also get them in 45LC but you can't run barn-burner rounds of the 45LC+P type - cylinder walls are too thin. So in 45LC you max out with a 255gr hardcast doing 1,000fps for a bit over 500ft/lbs energy. As a 357 this gun can shoot the "wild child" Buffalo Bore, Doubletap or Grizzly loads running as high as a 170gr hardcast at 1,450fps, energy up around 800ft/lbs. They aren't made in 41Mag.
The Rugers are the most complex.
The Ruger "New Vaquero" is a new mid-size gun similar in size and heft (and strength) to the Colt SAA or Beretta Stampede, so everything I just said about 357 and 45LC loads for the Berettas applies here.
The Ruger 50th Anniversary Blackhawk 357 is basically the same mid-size frame as the New Vaq, in 357 only, with adjustable sights. If you want adjustable sights in this class of gun it rocks.
All other Ruger Blackhawks and SuperBlackhawks made from 1973 forward are based on a larger frame size capable of 44Mag and above horsepower. In 45LC you can run monster ammo such as Buffalo Bore's 325gr @ 1,300fps "45 of doom" load. They were also offered in 44Mag (mainly SuperBlackhawks), 41Magnum, 357Magnum and other calibers. The "Hunter" variants are interesting as they have heavy 7.5" barrels with integrated scope mounts for scope rings (included in the box). Hunters were made mostly in 44Mag but some 41Mag and 45LC variants exist.
The "original Vaquero" is now discontinued. It was fixed sight, based on the same large frame as the Blackhawks, Hunters, etc. except fixed-sight instead of adjustable.
In the Ruger world, "Bisley" means it had a different grip, very low hammer and more curved trigger. This setup is well regarded for its ability to handle big recoil. You'll see Bisley Hunters, Bisley Vaqueros and just plain "Bisleys" which are basically similar to Blackhawks or SuperBlackhawks depending on caliber.
OK, how do you pick?
What's your need? Examples:
* "Fun gun/range gun": you're going to want adjustable sights for sure for playing with various loads. Probably a basic Blackhawk.
* Lower 48 states "woods/backpacking gun": probably run a 50th Aniversary 357 for it's smaller, handier size - a lot of this will depend on your hand size of course.
* Alaska-grade critter defense: you want a SuperBlackhawk in 44Mag, likely one of the shorter barrels.
* Boar/deer hunting: get a hunter
. On a budget, find a used SuperBlackHawk with a longer barrel (7.5" is common) as there were scads of these made and deals are to be had.
* Street defense/CCW: There's a 3.5" short-barrel "Montado" version of the NewVaq in 45LC that is just sweet. Lower SuperBlackHawk hammer. Speer has a 250gr really fat mouth JHP that does about 900fps or so that should be a superb stopper.
What else...
* Rugers are good guns, but they do make a lemon now and then. Use the "checkout procedure" (stickied post) to identify such even on a new gun. Average quality control and accuracy on the mid-frames (New Vaq and 50th Blackhawk 357) is actually higher than the large-frames by at least a bit.
* Parts swapping. You would not believe how much aftermarket stuff is out there for Rugers. Want to swap grip frames, hammers, sights, etc? Yeah. And parts swapping often works across different Ruger guns.
So which is mine?
Ruger NewVaq 357, 4.68" barrel with improved fixed sights and SuperBlackhawk hammer like the Montado (and I did that mod years before the Montado shipped). It's a daily carry CCW gun complete with "psychological warfare".
That said, I'm considering converting it to 44Spl. Reason being, the 357 (and 41Mag) need to be supersonic (WAY supersonic) to work well. That means big noise, big recoil. (Speed of sound is 1050fps or so.) The 44Spl, 45LC and 45ACP work great at subsonic speeds and of those three, for a number of reasons I'm going to go to the 44Spl I think. More cylinder beef available than the 45LC, bigger shell and less pressure than the 45ACP. This swap means finding a Ruger SuperBlackHawk 44Mag barrel, chopping it to 4", swapping it out and having the stock 357 cylinder reamed to 44Spl. It means re-doing the front sight again (sigh) but I want to do something more radical anyhow...
(The advantages of the 44Spl over the 45LC in an SAA/NewVaq size platform are very minimal. Since I'm in a position to pick at equal cost I'm going to the 44Spl, but new the 45LC "factory made" will be much less and a better idea in terms of price/performance. And there's some bichin' loads in that caliber...that Speer 250 alone may cause me to do 45LC regardless...)
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Oh yeah. There's one more transfer-bar SA. The Freedom Arms '97 frame. If spending $1,300+ doesn't scare you, it's a hell of a good gun. Ask about that if you're interested.