As far as brand goes I learned recently to believe what many many folks on here said about what mower to buy. DEMO, DEMO, DEMO. Secondly, who do you have around you that's close for a dealer/repair shop.
I think most on here use their equipment for their personal properties so a bigger engine/deck will be very useful on your place, but you have to look at what you're wanting to do on expanding. Another LCO I know says definitely go 60"... but I can't see on anything residential more than a 52. But again, that's just me. I have a few customers in a condo subdivision and there I wouldn't go bigger than a 48. I told my dad that if we had to do it all over again I would do a 36-42 walk behind (what ever size these things come in now-a-days) and a 52" ZTR. That would cover almost ANY situation you would run into.
Hope it wasn't too long winded.
Best Impressions Lawn Care - est. 1998
2 operations in different cities
(Expansion is awesome)
48" Grandstand and 52" Stander X
2 44" Toro WB's
Shindaiwa weed eaters
Stihl Backpack Blowers
Stihl and Husqvarna Chainsaws