I have a Craftsman with a 2 cyl. 24 hp B&S Intek that after 5 1/2 years, is running well, with only oil changes (Mobil 1), air filter changes, I fuel filter and 1 spark plug change, while the mower, of the Husqv model type made for Sears; front end, deck and deck supports), is falling apart around it. Not only the mower's fault, really, because I hit roots, cypress root stumps and small depressions (holes, removed tree areas, etc.) often. My back yard is a valley, with uneven erosion caused by heavy running water through an old deer path when it rains hard. Of late, I try to only use ethanol free gas in it and maybe that helps.
I can't imagine doing your yard on anything but a rider. Have you looked at the Husqvarna R 322 T? it is pricey, at $5200 list, but is maneuverable, can do hills, has 4wd, has a Front Deck (real good around buildings) and can attach implements. I'm, however, a bit worried about what it would be like hitting things.
I've been doing the walk-behind for 22 years. It's good exercise. I usually break it up into 45-minute segments (45 times three). I'm thinking of extending my cutting area, though. And, I'm getting older, so time is becoming more valuable!
I've had decent luck with the 8.5 hp Intek motor on my Troy-Bilt, but it rolled off the assembly line quite awhile ago. Comparing my old Troy-Bilt to the "new" Troy-Bilt has me projecting that comparison to B&S. The old Briggs built in America's Dairyland vs. the later ones built who-knows-where.
I don't want to spend more than $2500 or so. Home Depot has the 42-inch Ariens ZT for $2500, and my Gravely dealer has his version for $2700. They're the finalists unless I stumble across a deal on Craigslist. BTW, a local dealer has a pretty clean Toro SS3200 for 2 grand. Any thoughts on that model? At the suggestions of djdicetn I looked at the entry-level Dixie Chopper (Briggs motor) and the Hustler (deck raised by hand lever vs. foot pedal). Good options, but I think Ariens/Gravely look most attractive to me.