Unsure, which would be better or is it a personal taste thing?

I was thinking critical effects since it'll assist with both sword critical effects and magic, and because I like setting things on fire and it seems more interesting. However, I'm unsure if it's anywhere near as effective for putting out decent sign damage.
Also I've heard on hard difficulty setting enemies have higher resistance to critical effects.

I didn't know what I was doing on my Magic run.

I'll hazard a suggestion though. I think you will get more out of the Criticals, for just the reason you note. You still use your sword quite a bit with Magic build.