Como dizer "Carne macia, Carne dura" em inglês

Tender would be "carne macia/tenra" they are generally associated with being "flavourful/juicy" ones.
"Tough meat" is difficult to chew (since tough also means 'difficult'), sometimes people say "more inexpensive meat" as a workaround way to express 'tough meat'.
There are tenderizers (sometimes malets OR meat pounders) to tenderize the meat in preparation for cook, they are meant to 'emaciate' a slice or lump of tough meat.

As for "carne de primeira" we could be talking of "prime meat/prime beef" or "choice cuts" (também considerados carne de primeira, mas uma 'segunda linha' em relação às "primes".