AutoEurope also gives an extra (cummulative) 10% discount to bestfares.com members (for rentals of over a week that is a 30% discount). However be aware that their rates for cars are not necessarily better than rates that you can get with an airline discount number. For example with the BA AWD number available for use by all B335100 (also you get 1000 BA miles between Oct and Jan when using this number to rent with Avis) I got a slightly better deal for an upcom,ing trip on a Group K car out of Gatwick even with the bestfares extra 10% (actually a much better deal as AutoEurope charges 29 pound pickup fee).
Another word of caution re Auto Europe. When I rented through them a few weeks ago I rented what was described as a Rover 620 class car on their web site for $200(weekly rate). On the avis web site the rover 620 is listed as a Group K (luxury). When I got to Heathrow I was told that I had been booked in to a group F car (a couple of levels down) and had to upgrade to a group K for an extra 10 pounds a day(they gave me a Saab 9.5 and I was a happy camper as it worked out to a weekly rate of about $300 which given the car wasn't bad). A group K car to AutoEurope is a Merc (through Budget) and they will charge you about $460 weekly rate (so my SAAB through Avis was a good deal).
What is the point of these ramblings. Try the AWD or your own AWD number with Avis first plus any coupons (or another discount with another rental company first) and then see if Auto Eureope can beat it. Sometimes they can and sometimes they can't. and if you do a lot of renting through them you may want to invest in a best fares membership for the extra 10% off.
PS you still get FF miles when going through Auto Europe but keep an eye on their fees.