Northwest Visa by U.S. Bank.

Keep spending until you're blue because there's no monthly limit and no annual limit. Beyond $10,000/month or $50,000 per year ($80,000 for Signature Account) you still get a mile for every $2 spent. Before you reach the maximum, you get one mile per dollar spent.

Point Conversion Fee is zero.

Using the "Mileage Conversion Rate" (MCR) of 1.25 cents per mile you need to charge 4400 dollars per year to break even considering the annual fee is $55 (or 7200 dollars charged at the $90 annual fee). When in doubt, don't pay the annual fee and conserve cash.

One other drawback about Northest Visa is that you have to fly Northwest.