There are only two such card programs, and one you're trying to get out of (Amex MR) and the other one is not taking new card apploications at the moment (Diners Club).

If you only use miles for coach flights, then one of the "fake miles" cards may work for you. But they're useless if you use miles mostly for int'l premium cabin flights.

Which leaves only hotel cards. Since most hotel programs allow you to transfer into a variety of airlines, a hotel card would give you only one hotel (thus not the same flexibility on hotels as Amex MR or Diners Club), but would actually give you a wider variety of airlines than either Amex MR or DIners Club alone (since they have only slight overlap on airlines).

If you don't mind an Amex that's not MR, the best would be the SPG Amex from Starwood, as it earns 1.0 to 1.25 miles per dollar. $45 annual fee (waived first year).

If you want an MC/Visa, the best from a miles earning perspective might be the WyndhamRewards MC, because it earns almost 1 mile per dollar (while most other hotel cards earn closer to half a mile per dollar). The upside of this (and most other hotel MC/Visa cards) is no annual fee.

Most hotel cards from "nicer" hotel programs, other than SPG, earn fairly few points except when you use them at the hotels themselves. That's why they only get you 0.5 miles per dollar at best. WyndhamRewards gets you more miles only because they have an unusually rich hotel-points-to-airline-miles conversion chart. (WyndhamRewards is mostly a collection of cheapo motel chains like DaysInn and Super 8 so redemption for hotel nights in that program may not be your cup of tea. I mention it only because it's the best value in an MC/Visa I know of earning "fungible" miles if you don't want Amex MR and don't already have Diners Club.)