I found Auto Europe to be the best deal when renting in Ireland also. We had no problems with them, and it was a good experience. It's always important to read all the fine print when renting a car.
There is an issue with insurance and Ireland that needs to be well-understood. Some built-in credit card insurances will not cover Ireland (I don't remember all the details). I also noticed that different companies classified car sizes differently, so that you might think you are comparing 2 cars of the same size from 2 different rental companies, when one is actually quite a bit larger. Auto Europe wasn't any worse about this stuff than other companies. It just seems that car rentals can often end up costing more than expected with extra surcharges, etc.
Many have had success with Auto Europe, including Andi. I haven't personally used them since I usually get my lowest price from Kemwel. Do take a look at my "Car Rental Page" because it will give you a good idea of insurance, lingo and what to do before renting.
They are both brokers. Meaning they don't have their own fleet of cars but merely shop the other companies and get you the best price available. I use Kemwel all the time and am very happy with them. If you click on the link to Kemwel on my "Car Rental" page I will get a tiny bit of each booking but you will pay no more. It helps me keep my forum and website operating.
I've used Autoeurope in Itally a couple of times and was very pleased. Always got the car we requested. As Michelle said, they are just a broker, so once you book and pre-pay the rental, they send you the voucher and it will tell you where the car comes from. One time I got it from Europcar, one time Avis. It all depends on where the pickup location is.
I noticed while researching my Ireland trip that they offer 2 or 3 different downtown pickup locations for Dublin. One of these is an identical address to Avis. I can't figure out who the other one is.
The key for Autoeurope is they make you pre-pay for the rental in its entirety. This is part of the way they make up the price difference...they collect interest on your money from when you book the car. not a big deal, just something to know.
Good advice! Just a note about Kemwel. They tell you who the rental will be with up front. If that is important for your plans it is just a bit more info that you have.