I would expect that open source developers will best know the implications of GPL and MIT licences, with LGPL, BSD* and Apache2 following next. I have personally never head of Unlicense before even though I was involved in many open source projects.

However, using CC0 probably won't do much harm either.

I wouldn't be nearly so scared from just using the MIT licence. It's simple, nearly everyone knows it (because a huge amount of projects already use it) and it's easy to google for whoever doesn't. Don't do something exotic if you actually don't have specific needs.