At risk of being sued by G7 I've got to say again please check their website carefully before you buy. I believe the initial problem with G7s is now fixed, but I've had too many fail on me ever to trust one again - and I know a lot of others who agree.

Kyser is the only capo I know which has sufficient tension, and which also always falls flat to the strings. It's nice and narrow too so you can park it just so. I have a slightly higher action than I should because I need the volume to work against banjo (played with a plectrum) and twin-course instruments (also), so Dunlops are not reliable (their spring is a little weaker than the kyser).

Kysers require practice to get on and off (in fact they're darned awkward) but you'll find them safest for tuning.

Remember that no guitar is ever perfectly in tune - it's always a compromise, and that compromise needs to be adjusted acording to what key you're in and what you're playing, which is why we all waste so much time faffing about between numbers. The capo is an additional complication.

Tuning is most critical in duos. In a session or band you can get away with murder, and solo you can drift as long as you're in tune with yourself. But in a duo both players need to be cock on to make the instruments really sing - so this is a subject I spend more time thinking about than any other!