This will be a great place to get ideas on best zt options. Hard to recommend without budget you are tied to. Things to consider
1-a trusted dealer for quality service.
2-hydros 2800, 3100, 3400+
3-engine (kohler vs Kawasaki vs b & s)
4-deck fab vs stamped/48 in, 50, 60, 72?
5-did I mention trusted dealer?
6-seat/suspension for ride comfort
7-residential/prosumer/commercial mower as there is a definite difference in price.
8-purpose or yard(s) are you just mowing your yard or are you going into business?
All the bigger names (toro/Exmark, ferris, gravely, hustler etc) will all offer a quality mower so it will get down to personal feel and budget. Also, like myself, those who like the mower they bought and can give you opinions on their brand of choice. For instance, I am an exmark guy. Dealer and quality were I biggest reasons. I suggest you find all the dealers local and ask to sit on and demo each you are considering.