I use a net if I have to. But I think about it before I do.
If it's a big fish, use a net if you have to.
If you are fishing for dinner, use a net.
But if you're just doing C&R, bring them to your feet, kneel down, de-hook, let them rest, send them off.
Mortality from 30 seconds of "breathing air" is around 38%, even if they swim off.
Mortality from 60 seconds of "breathing air" is around 70%.
If that fish has to come out of the water for any reason, start holding your breath.
When you give up, give that fish a drink! (from TenkaraGuides.com)