We were a group of 5 and had rented an SUV, standard size. We mistakenly figured an SUV that would fit five persons would also fit luggage for 5, despite it saying 2 bags, but we decided to stick with what we ordered even after barely getting everything in. (Might go for a larger SUV if prices were lower*.)
Note: It was a good thing we didn't actually try to get a larger SUV. While it may have been a bit more roomy, it might've been impossible to drive through the tiny streets and garages we eventually drove through. As it was, we barely squeezed the Cupra into relatively tiny parking spaces and past other vehicles.
Our interaction with the agent was great! She (I think her name was Julietta? I can't remember for sure, but something with multiple syllables and very pretty) was very nice, let us add a second driver (easy process), and for an additional 30 euros (might've been only 20), said we could return the car to the Dublin airport rather than back to Q-Park, which was a huge relief.
We also (based on renting in a foreign country, and suggestions from friends) got full coverage insurance from Sixt, not depending on our credit card or Expedia insurance to cover any damage that might be done to the car. It was about an extra $100/day, but well worth it. A friend who'd been to Ireland just a few weeks earlier said her husband, who is a great driver, lost a mirror, and thanks to full coverage, there were no issues upon car return.
The Cupra was awesome! It was a hybrid, so didn't cost as much in petrol as it could have. It did have some automatic features, such as switching between high and low beam for night driving, which we loved. And auto windshield wipers if we didn't get to it quick enough, lol. She was a really great car and fun to drive.
We did get a warning for low tire pressure (we refilled each tire, but the message never went away for some reason, and the tires never flattened), and a warning about the battery part of hybrid needing a recharge, but neither of those things caused us any issues, and we never needed to use roadside assistance.
When we dropped off the car at the airport, the agent noticed that one of us had run up against the curb and caused slight damage to the tire rims, but said since we had full coverage, there would be no cost to us. Credit card is still extra charge free, and I'm assuming it will remain so. Only charged the cost of the car, insurance, and post-rental fee of $3.68 (after conversion) for driving on the M50 (which does not take cash or credit, but relies on license plates).
Anyway, overall, we had a great experience. Would rent from Sixt again.
*The price for an automatic car rental in Dublin is absolutely insane, at least when we went, and a larger SUV would've cost at least an additional $700 for 3 days. As it was, a 3-day rental was over $1600 (including rental and full-coverage insurance), but that's not Sixt's fault; it's supply and demand. Every other rental agency was even more expensive, and for smaller vehicles. (I did just look to see prices for a similar rental period in the future, and the price has gone down tremendously. Only $635 for 3 days, before insurance. Boy, did we go at the wrong time.)