I work at Air Canada

Westjet is good, but the only reason why I'd prefer AC as opposed to WS as a passanger is in case of delays/cancellations where Air Canada is better able to handle them (since we operate a greater number of flights). But otherwise, I've heard great things about westjet and their service.
Another thing, if you really want the best service, then you can't go wrong with Air Canada's Executive class with access to the Maple Leaf Lounges. In case you haven't been to the lounges before, they're kickass. Free drinks (alcoholic and non-alcoholic), Free Wi-Fi, Xerox business centres (private workstations with fax, photocopy and colour printing).
But other than that, for that 10$ difference I'd expect you should pretty much get the same service from both airlines.