DTAG rental fleet convertibles are usually Mustangs or Sebrings. I've gotten both; it's luck-of-the-draw.
I actually didn't like the Mustang convertible. Uncomfortable seats, lackluster engine (they're base models), mediocre audio system, etc. I actually prefer the Sebring over the Mustang.
I haven't rented a convertible in a couple of years, however.