I've owned 3 of the 4 (Z3, Z4, Z4M, and 987 Boxster S), and there was some overlap
Short version: the Boxster was better day-to-day, the Z4MC was better as a weekender, being more focused but harsher. Brakes were better on the Porsche. If I were choosing now, at 60, I'd get the 987S; in fact, I plan to when I quit riding motorcycles.