Ward per second, on potion use, or when hit?

I’m having a hard time understanding which is the best, or under which conditions one might be better than the others. Anyone have any input?

I’m thinking ward per second might be the best because it should always be up, even if the amount might not be as high as one would get from the other two sources.

Also, the one on hit … I’m not clear on whether or not that ward is applied before or after the damage is applied. If it’s applied before the damage is applied that might be useful, but I’m not sure how useful it would be to have it applied afterwards. Etc.

On potion use could be useful for builds that use pots for triggering other things as well, in which case you’re building off that symmetry, like the Zerrick set build I posted a few months ago.