After the first six months free with the AA Mastercard, it's only a few dollars cheaper than the Diners Club card.
Diners comes with 12k miles (actually 24k Club Rewards points) signup bonus in the first year.
Diners will be the #2 card as far as I'm concerned once the Mastercard acceptance is phased in (and provided they don't devalue the Club Rewards program)... #1 will still be the Starwood Amex.