Generally, I don't kill them at all, just make vulnerable plants harder for them to get to, by standing pot plants in trays of water or up on raised areas or by using copper.
I can live with a bit of slug damage.
The only exception is with young seedlings vulnerable to slug attack - where I do apply a light scattering of ferric phosphate pellets A small bottle lasts me at least two years, because I hardly ever use them.
I think opinion is generally divided on two counts:
1) TO KILL OR NOT TO KILL
2) IF YOU ANSWERED 'TO KILL', THEN THE SECOND POINT IS 'HOW TO KILL'
When it comes to actually killing slugs, the more squeamish of us would probably shudder at the thought of squashing a slug and seeing what we've done, whereas when you poison a slug, it potentially suffers as much or more, but we don't have to see it.
Personally, I don't think I could bring myself to stamp on them or snip them or anything like that... then again, I squash aphids and mealybugs, so I guess that makes me a hypocrite.
And I love snails - certainly can't bear to kill those. I feel guilt-ridden for ages if I accidently tread on one. That dreaded crunching sound....
I remember going to a restaurant one evening for my birthday with my family. When we came out to go back to the car, I found dozens of snails making their way up and down the stone steps of the veranda, around the pot plants. Many had been crushed and a woman walking ahead of us crushed one (accidently I think as it was quite shadowy) with her high-heel, which made me wince.
So there I was, in my best clothes, bent down gathering as many snails as possible before the next diners came out and removing them to a nearby hedge.
The family realised that I was no longer with them, so came back to look for me and hastily started gathering snails too (realising it would be ages before we got home if not)!
I'm not barmy or anything....