Pop. Well more of a hiss than a pop. The car we rented whilst in England recently had a slow puncture in one of the tyres. Avis were excellent - I called them and explained that it wasn't worth a breakdown call because I could get back to the airport for an exchange. The girl assured me there would be a car for me when I got there, so we bumbled back up to Gatwick. Sure enough they knew I was coming and had a replacement car ready to go. The slight sting in the tail? Because I didn't do fully comprehensive insurance with them, I had to pay a flat (pun intended) £89 fee for the replacement tyre. In retrospect though, their fully comprehensive insurance only brings the deductible down from £800 to £100 so it wouldn't have covered the tyre cost - I would still have had to pay. No biggie - it was an expense we could do without, but Avis dealt with it courteously and promptly. That's a lot more than can be said for some of the issues I've had with Hertz at Gatwick in the past.
+1 to Avis.