Last night I visited Reliable Medical to test drive a few wheelchairs. I'm 99% sure I'm going to go with the Quantum Q6 Edge, which sounds more like a car from Infinity than a chair.
If the manufacturer's web site is correct, driving a Quantum chair f*cking rocks! Visit their home page & click the "Q6 Feel the Power" link. You'll see a guy tearing through gravel and zipping along uneven pavement while a Steve Vai-esque soundtrack blares.