Goldcar will probably ask you to return the car filled as received, and it is not a full to full situation but could be part full - which I find deeply irritating. Keddy is actually Europcar's budget product. I have no personal knowledge of the others although I have heard of Centauro. I would not hesitate to hire from a less known company but I would always go armed with my own excess insurance (google it) because all of them charge silly prices for zero excess. It is of course important to be sure to record any damage (including inside) when taking charge of the car - it is easy to take photos these days, but I have found that, by the way inspections are often only cursory on return, rental companies do not seem to worry too much about the odd nick (although I have never added any).