boil bottle caps or soak them in sterilant?

soak them in start san for 1 minute. if you boil them, you might ruin the plastic seal. if you baggie the ones you dont use, you can use them next time without re sanitizing.

just use growlers, its faster and you dont have to use the capper.

If you are talking about bottling your own, I'd use a mild sterilizer you can buy at a brewer shop. All you need is some neutral cleanser, which is usually used in conjunction with hot water. The guys I buy my brewing stuff from told me boiling does not ensure you have killed all bacteria. You don't want to have funky stuff in your bottles, it'll ruin your batch.

I put in a link for my Brewer shop... Use the stuff called "One Step"

dont ever boil caps.

you will ruin the seal inside the cap

use one step or idophor solution

Either way is fine, the point is to keep out microrganisms that may spoil the brew.