We went through a similar discussion, we're based in England so the easiest for us would be to charge £ but we went with $ because we figured that:

* £ would likely put off Europeans & Americans

* € would likely put off Americans but UK would be more used to it

* $ doesn't put off UK or Europeans as while they may prefer their own currency, they are used to paying in $ for subscription based web services.

Ideally we'd let the user pick their own currency, but having to handle fluctuations & keep constant pricing wasn't something we fancied figuring out for launch. Also more currencies cost more to support.