One of the best one acre mowers use to be the Hustler 42" mini Fastrak. However, it is no longer in production. They now make the Hustler Sport. I would say that the Hustler 42" sport would be a good choice. Also the BadBoy MZ 42" would be another. I think as someone already mentioned, a little more info on your property and budget?
Hustler SuperDuty 42" 19hp Kawasaki KAI
Stihl BR-600 Magnum
AMSOIL In Everything I own