There are the 5 I have heard of.
Taylors & Co
I wish I could try them all to test it out but I am wanted a 3 1/2 barrel shooter with a smooth trigger! Any recommendations?
I'm a little late to this party, but will throw in my two cents.
Personally, I would knock two right off your list - Uberti and Cimarron. First, they are the same gun. Cimarron, simply takes an Uberti gun, makes some modifications and resells it. It is not a _bad_ gun by any means. I just think the others on the list offer a better value for the dollar.
Taylor makes a short barrel gun for mounted shooting. I forget what it is called. I haven't seen or help one, but several people have told me very good things about it.
I have worked with Rugers and Colts. Both are excellent guns.
Colt is the Rolls Royce. Great gun, but you pay for it. Not only about $1200 per pistol, but it will also need some tuning work out of the box. You are actually paying around $1500/pistol when all is said and done. Expensive, but then again, you do have a Colt.
Ruger is my personal choice. Built like a rock. Drop it in the dirt, have your horse run over it... brush it off and it is ready for the next stage. These things are built to last.
As mentioned, you would be looking at the Ruger Vaquero (formerly known as the "new Vaquero").
If you can find one, I would recommend the Ruger "Montado." Costs a little more and is much harder to fine. It has the 3.5" barrel and a gnarled, truned down hammer. All the women shooters I know definitely prefer this gun over any other. (Note - the Taylor has some of these features and may by easier to find).
Regular grip vs Bisley or Birdshead grip - this is a matter of preference. I suggest trying each extensively to see which your hands like better. It stinks getting stuck with a grip style you don't like.
While I love the look of case color, I highly recommend getting a stainless steel model. Black powder is murder on metal. Stainless is much more forgiving and easier to clean. When my guns get really dirty, I just put them in the dishwasher. You can't do that with a blued or case color finish.