What is the best credit card for earning airline miles?

credit cards that earn airline miles

First thing to watch is liquidity.
When you gain miles by flying, they are tied to the affiliate program you fly in, and sometimes you find yourself with insufficient miles in different accounts.

Airline cards accumulate miles within their program (star, sky, aeroplan).
Non-airline cards accumulate miles in their own account, which you can transfer to affiliate programs. This extra liquidity is a great advantage so I'm looking only at these cards:

• AMEX Starwood Preferred Guest:Transfers to Sky airlines at 1:1, Star at 50% loss. Spending $1 gives 1.25 miles. 
  $65/yr after 1st year. 25K miles intro bonus.
• Chase Sapphire Preferred:Transfers to Star at 1:1. Spending $1 gives 1.07 miles, X2 on dining and travel.
  $95/yr after 1st year. 50K miles intro bonus.

And the special one:

• Capital One Venture Rewards:This card miles' can travel with any carrier booked anywhere, Capital One simply deducts miles for dollars in your credit statement.
  Spending $1 gives 2 miles which fund $0.02 for travel. 
  Compared to real airline miles, that's a better deal for domestic flights but not for int'l. 
  Pro: liquidity is just like real money, you can use it for a $60 flight on Southwest, while Delta has a minimum price of 25K miles.
  Con: the miles cannot be transferred to airlines so they can't top off the account when you need it.
  $59/yr after 1st year. 25K miles ($250) intro bonus.
• Conclusion:
• Big spenders get the AMEX SPG, most liquid airline miles for the dollar.
• Moderate spenders get the Chase SP, fat intro bonus buys a coast-to-coast flight.
• If you fly cheap often, i.e. many sub-$200 tickets booked via online hunting, get Capital One VR.