You need to decide, before buying anything, what you want to do.
Do you want to play cowboy?
Or do you want to win?
Many people start off - they want to play cowboy. So they buy 44s or 45s, because "Cowboys used big guns". Problem is, big guns recoil more, and getting back on target takes longer. 45 shooters can't shoot as fast as 38 shooters.
If you want to win, go with 38s. Lighter recoil means faster back on target means quicker times.
If you want to win, go with Ruger. They hold up better than Colts or US Fire Arms or the Italian copies. Nothing against the Colts and their counterfeits (as Col. Colt used to call 'em), but Rugers are stronger, and in a speed competition, a stronger gun does not break down as much.
You want real speed from a rifle - get a Henry-action - the 1866 or the 1873. They can be made to run faster than the Marlins, and than the Brownings. And for sure stay away from the Winchester 94, because that hermaphrodite cannot go fast. And again, go 38.
Seems like all the really fast people with a shotgun use a 97. But I've heard you really need three - one to shoot, one for backup, and one in the shop being fixed.
Of course, none of that applies if the CATEGORY you wish to shoot in has gun requirements.
Classic, for example. Guns HAVE TO be 40 caliber or larger. Rifles HAVE TO be 1873 or earlier - which means no Browning-designed 1892, no Marlin 1894. Shotguns HAVE TO be either a hammered SxS or an 1887 lever-action.
But if you chose Movie Cowboy, you rifle HAS TO be a 92. The 73 and 66 aren't allowed.
Those are some things to consider.
Me - I never COMPETED. I had no expectation of winning. I PARTICIPATED. I shot 44s, either 44/40 in US Firearms or 44 Russian in a Uberti #3 Russian. My rifle was usually a Rossi 92, in 44/40, but occasionally it was a Spencer in 44 Russian. And I shot SxS shotguns with exposed hammers, underlever opening, and long barrels.
I wasn't fast, but I had fun playing cowboy.