From the factory you have the single six and single ten (single nine as well if you add in WMR). Borchardt offers an eight round replacement cylinder for the single six, but I've heard tell that they have some issues. Just comes down to what your looking for.
I have both for different reasons. If you think you'd use the magnum cylinder the single six is the way to go with the caveat that short barrels and 22 magnum have given me nothing but fits as far as unburnt powder gumming up the works in less than a 5 1/2" barrel. If you are only going to shoot 22lr and like unfluted cylinders the ten is great.
This is my boys 60th anniversary convertible after his uncle tweaked it up a bit. Still needs a little fitting on the grip frame to mate to the horn grips.
This is a single ten I got to make a matched companion to my Talo super. I needed an unfluted 22lr cylinder. the single six Bisley hammer worked out just fine in the ten, only need to swap over the 10's pawl on to the Bisley hammer.
Still fitting an xr3-red short frame and need to cut down the stags to fit, plastic fantastic in the mean time. Shorty 44 and half pint the Shorty 22.
This old model is next on the chopping block when I get the current projects done. Converting to centerfire, fitting a 32h&r cylinder and barrel cut to 3.75" with a dovetailed front sight, and adding a brass birdshead frame. Did a little mocking up before the last parts came in. Stainless ERH will be replaced with blue steel. Should make a nifty back pocket barn gun.