Here's the official list of the companies serving Cork Airport:
http://www.corkairpor...airport/car-hire.aspx
I can't find consistently good reviews for any of them!
Part of the problem is that there are actually very few car hire companies. For example, Avis & Budget are part of the same company. Similarly, Enterprise and National Alamo are just different trading operations of a single firm, and Hertz took over Advantage.
Your best bet is probably to use a price comparison site to find the best deal
http://www.travelsupe...ar-hire/ireland/cork/
and then to cross your fingers!
Chris