Well, when I was just getting started in CAS, before a burst blood vessel in my eye put an end to that, I got two 44 Vaqueros, and two Cimarron Model Ps, also in 44, albeit Specials. I just prefer booms to bangs I guess. 357/38 is "king" because of speed (no recoil) and costs, but I still saw/see a lot of the really good competitors using 45 Colt, so don't be deterred if you like bigger too. I got 7-1/2" barrels, because I like 7-1/2" barrels, and because I knew there was no way I was ever going to practice enuf to challenge any of the really serious cowboys anyway. That was several years ago now, and I am planning to sell one half of each pair real soon, and the shotgun.
As far as drawing the revolvers, a buscadero style belt is much more practical to me with longer barrels, and I was used to wearing one for years anyway. If period correctness is your meat, than I would stick with 5-1/2" or 4-3/4" barrels.
If you go with Colts or clones, better plan on 3 guns, because you will need a back-up if you shoot them a lot. Rugers, whether fixed sight Vaqueros or adjustable sighted Blackhawks, will outlive most of the competitors. Of course you may want to get the four click Power Custom hammer/trigger, and the free spin pawl, and the Belt Mountain cylinder pin, and Gunfighter Grips, and Wolff Springs. Oh yeah, and a "professional" action job. If you resist the hype you can decide as you go what you really need. The Ruger works right out of the box, but you don't have a lot to talk about.
Have fun, and do what you like to do.
