I plan to rent a car for a week in July in Ljubljana Airport. I have never rented before so doing my homework and reading forums not to get burned by renting from cowboys. I have been quoted £77 by Sixt for six days which is cheaper than Hertz (£114). I am not sure which company to go with. Here are the thoughts that i picked up on the internet:

Hertz is expensive but has a good reputation and is good at dealing with problems. There are almost no complains on Hertz forum on Flytalker as opposed to the Sixt forum which is full of desperate customers.

With Hertz you pay what are quoted online. Sixt tends to overcharge a lot? Or am I wrong?

How much more than the quoted £77 should i be expecting to pay when renting from Sixt? There is a 10% airport charge, highway toll, anything else? Would like to take a third party insurance. Could I turn down Sixt insurance and use my own?