I’d struggle to pick just one! It does matter whether you have a G1 or G2 Contender or an Encore, as the pressure tolerances of each are very different.
There tend to be 3 types of TC/specialty pistol type shooters, and you kind of have to decide which you want to be:
1) The “a pistol is a pistol guys,” which will pick pistol cartridges because pistols are pistols and should shoot pistol cartridges. Hence 44mag, 460, etc. Nothing wrong with this, but cases are still small and velocities and BC’s still low, so the max range remains inhibited. They work, but they’re still more limited than the platform could be.
2) The “powder burn efficiency guys” which are focused (too much) on the fact the barrel is short. These guys pick things like 308win or 358, 7-30 Waters, 30-30, 30 or 357 Herretts, 300blk, 7.62x39, 45-70, 444 or 450 Marlin, etc which have low expansion ratios - which is effective in reducing blast, and does still extend maximum effective range on game, but they still give up some performance.
3) The “drag racers” which are those of us which are performance focused and worry less about blast. We’ll pack an Encore or a bolt action with a huge cartridge and get the most range out of the platform. Big blast and big recoil, but big range. These are things like 6.5 or 6 creed, 300win mag or WSM, etc.
Personally, I’m in group 3, so I’d lean heavily towards a 300wsm or such if I were to only have ONE barrel on a TC.