We loved our Sixt rental car: a Toyota Yaris. Two of us fit very comfortably, with a huge amount of baggage—our usual modus operandi. The car handled well and was the right size for Irish roads, which are very narrow. The rental price was quite fair, and the gas mileage was amazing—we traveled all over western Ireland for a week on 33 euros of gas!
Car pickup was easy and friendly. Car drop-off was difficult: we followed signs to rental car return, but that was the wrong place, per a staff member there. Finding the real return area was super-difficult: you had to go through short-term parking and get a ticket for a free 15 minutes, then find the Sixt lot from there. No signage whatsoever. A Sixt employee who happened to be at another incorrect spot jumped in our car and navigated to the right spot, and we almost missed our plane! But all's well that ends well, and drop-off became one of those memorable travel adventures!