I'm assuming this will be the drive for what used to be the Robo Challenge house-bot?
I've never used a Sabretooth but have heard mixed reviews (although their customer service is excellent); I would tend to opt for a Scorpion XL/XXL, they seem to be a bit more robust for robot combat applications.

BUT, yeah don't use either for wheelchair motors. Get some heavier duty controllers. BotBitz 85s/self-programmed Turnigy 85s, as Gary suggested, are pretty sturdy and low-cost for the size of application.