Some business belong to association that can offer lower rates to businesses and single establishments.
Currently as a single establishment through a wholesalers association we pay:
We had AMEX first and they would take 4.5% and after a while with a little volume they dropped to 4% .(BFD)
When I first started in business AMEX was the only card company that would give us a break and the abiltiy to accept CC. Once we had them then Visa and MC said 'Oh, you have AMEX, then sure you we can help you'
In my experience AMEX also was very hard to collect from, in some cases it took a week to have the charge hit my account.
Personnally I have a Visa that collects AeroPlan Miles (Air Canada) and a MasterCard for AirMiles and the one I like better Canadian Tire MasterCard that collects Canadian Time Money