I will add a little bit more:
PofA is specifically an organisation for Americans. UNIMA however is an international organisation, which has branches in many countries. For instance, I have been a member of UNIMA Australia; there is one in New Zealand; France is the HQ.
It's dependent on location, but UNIMA seems to be very similar to PofA, with the exception that the latter also has state guilds whereas UNIMA centres tend to only represent the country as a whole.
Technically speaking, being a member of your local UNIMA centre should also open up the ability to apply for UNIMA grants that are not necessarily country-specific. Ie. as an UNIMA USA member you could apply for grants offered by the HQ but are not offered directly by the USA centre... such as international travel grants or awards where one person is picked from a global submission process. That obviously may have added benefits

Both also may have festivals, but UNIMA has a regular four-yearly one (this year it was/is China) which is presented in different countries every time. Being an UNIMA member in your country means you can also apply for UNIMA registration rates at these events; no matter which country the event is taking place in or which country you come from.
(Not to push UNIMA necessarily, I've just obviously had more experience with my local branch than with PofA)