Avis - Avis Luxury (N) Vehicles at LHR

Hi,
I have a pre-paid booking for July at LHR. I got a great rate from carhire3000 for around GBP980 for 28 days in a Luxury. The Avis website says its a Mercedes E200 auto. Has anyone rented from this group ? and any ideas what else is available?

Only other car you might end up with is a BMW 5 series (520d).

I picked up a diesel E200 auto from LHR last month. I think the BMW might be the better driver's car, but I appreciated the Merc for our long drive up to Scotland. Exceptional fuel economy too... cruised most of the way at 80mph and still returned 50+ mpg.