Hire was arranged through our Libra rep after we arrived in Kefalonia.
Thrifty gave very efficient service. We were told the car would be delivered to our door (in Trapezaki) between 9:30 and 10:30 and it arrived at 10:00. The car was a very clean and well-kept Hyundai Atos which, although it was small enough to deal with some of the island's more interesting roads, I found I could drive comfortably (and I am 6ft 7 tall!).
In the later part of the season, they had an offer of an extra day free, for over three days' hire, but I am not sure how their prices compare with other hirers.
No problem with returning the car - it was picked up from our studios, and no fuss was made about the slight redesign that I had made to the car's paintwork, coutesy of some very scratchy bushes on a very narrow road!