Travelers who pay credit card bills in full each month may benefit from airline miles and points. However, at least two airlines, Southwest and United, are now introducing debit cards that offer mileage rewards.

These debit cards often come with high transaction fees, and the rewards are generally worse than those offered by even the least generous mileage credit cards. For travelers carrying balances on credit cards, interest charges can quickly outweigh the value of any earned miles.

For most consumers, traditional debit cards or carefully managed credit cards remain the safer option.