I also have the AMEX blue for business when the offer was double points for the first $50K and 30% at end of year- effectively 2.3 AMEX points per dollar charged. If you use this in combination with the AMEX business platinum, which gives you 50% points back on the airline of your choice (American for me) or in business/ first, you are essentially getting 4.6% back, with the service fee of 1.87% this is a 2.73% margin!!!!

If you weren't able to get the AMEX blue for business, as mentioned the AMEX everyday preferred if you do enough transactions per month (30?) you get 1.5 MR points per dollar. Coupled with the AMEX business platinum with the logic above, you get 3% back which is still a very nice 1.23% margin.