Ah...this comes up often
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First thing, you need to decide whether or not you want a modern transfer bar ignition in what otherwise looks "period correct". The transfer bar safety prevents the gun going off if dropped, slammed on the hammer, etc. With a transfer bar, the gun is safe to carry "all six loaded". Without, you carry it "five up" and hammer down on the empty.
So far three guns are shipping that have the look and feel and (at least pretty close) heft of the Colt SAA: Taurus Gaucho, Beretta Stampede (including "Stampede Marshall" and a Bisley variant) and the Ruger New Vaquero.
The Ruger "Old Vaquero" is discontinued. It looked like a Colt except it was built on an oversize 44Magnum-class frame and beefier cylinder. If that's what you want, they're still out there.
The Ubertis are closer to a real 1873 Colt and lack an effective safety. To my mind, such pieces are OK if you're willing to respect them but if you're going to press the gun into street carry you want a transfer bar, and I can make a case for one in home defense and woods carry roles too. The Ubertis are imported by a number of companies, some of which tune them up and add a better warranty with stateside support - Cimarron is well known for this and sell Uberti-based guns in a variety of states of tune all the way up to the extensively reworked "Evil Roy" series.
Beretta bought Uberti recently. The Beretta-brand SAAs are Ubertis but with a transfer bar lockwork added and a high quality level specified. They're good guns and have one thing the Rugers lack: like a period gun, the Beretta loads on the half-cock.
The Ruger New Vaquero is Colt SAA-sized, but internally is a lot different. Coil springs are used throughout (more reliable than flatsprings) and they load with the hammer completely down: just open the loading gate and go. The New Vaqs at least "click" each time the cylinder rotates to a load position (chamber centered in the loading gate). The Old Vaq and all large-frame Ruger SAs annoyingly click when the cylinder bore is halfway past the gate.
The Taurus...well...look, I don't have actual experience but a LOT of people have complained about the Gaucho in particular breaking. Otherwise it's a lot like the Beretta. Personally, I'd buy the Beretta over the Taurus if I wanted maximum authenticity.
What I actually DID buy was a Ruger New Vaq. Quality control on these has been VERY high, better than most previous Ruger SAs. Mine was one of three I examined in 2005 at a dealer and all three were "tight and right" - close cylinder gaps, good alignment, good overall fit'n'finish. At the range mine (a 357) immediately showed it's worth, with windage dead on and elevation a hair high ready to be dialed in for my loads, just the way an SAA-class gun should be.
The good news with the Ruger is it's parts-compatible with a lot of the rest of the Ruger SA product line. Mine now wears a lower-slung SuperBlackHawk hammer and I had the sights improved custom for a better picture - dovetailed Novak front with the rear channel hogged out to match. Other action parts can drop in and the grip frame can be swapped for Bisley, Bird's-Head and the like with easy-to-get and often aftermarket support unheard of in any of the others.
The flaw: the Ruger New Vaqs in blue have a fake color-case process on the frame. It's not that bad looking but it's obviously not real. At least they've tuned the chemistry so it doesn't attract rust (unlike the first time they tried this on the Old Vaq). There's been a special distributor run of all-blue New Vaqs (from Lipseys I think) that you might track down.
Another option: Ruger has an adjustable-sight version of the same mid-frame gun, in 357 only, no fake-case, called the 50th Anniversary Blackhawk 357. It's a good gun if you want to play with varying loads a lot
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My answer was to dial in my sights dead on for loads in the 135/140gr range and make adjustments from there.
Upshot: if you're into modifying your guns, the Rugers are a home-tuner's paradise. If you want ultra-traditional, think Beretta for a transfer-bar gun, Cimarron otherwise.
NOTE: so far I've assumed you're looking for something $550ish or less. In the "grand or more" category there are really good (and good looking) pieces from USFA, STI and of course Colt themselves.
But, I would not be
