One finger with V's and discs, provided I can get the brake levers and gear levers into the correct position on the bars for both to work ergonomically
Having adjustable mounts on the shifters makes mounting them and the brakes both ergonomically much easier, as does having 700mm wide bars
You can just about make out my brake and shifter set up in this pic
Older non adjustable mount shifters make it trickier to achieve this as do the ones without the removable shift indicator window (generally on SLX and above)
With my Canti braked bike it's 2 finger braking, for a couple of reasons, one being aesthetics and the other power
try rotating your brake levers upwards so that your wrists drop a bit, if your brake levers are in line with your arms then your set up is a little out, it's a roadie thing having the levers in line with your arms.
Rotating the levers upwards will push your wrists down a touch which will help in both control over rough terrain (your wrists won't naturally want to pop off over the top of the bars, they'll push into the bars, if you see what I mean) it will also help relive arm pump and wrist ache (or it did for me)
A little test to try if you're not sure about rotating the brake levers up.
Stand with your bike by a kerb, with your hands on the bars / brakes & push the bike into the kerb (don't lift it, just push in a straight line), the bike will give some resistance to the kerb as it rolls up it and your hands may pop off over the bars
Then rotate the levers upwards a bit
Then repeat the above kerb test. You should notice less resistance as you push the bike into the kerb and your wrists will stay put as the bike rolls up & over the kerb
It's all physics innit