I am in the market for the same size machine. For me, this is a tough choice. I am unclear if the ZTR's you find at Home Depot / Lowe's are the SAME machine you can purchase at a "dealer" ? When I bought my JD ZTR425 (10+ years ago), there were many visible differences, so I ended up purchasing from a JD dealer. Today ? I cannot tell. My suspicion is that big box retailers *might* request builds using cheaper components that are impossible to determine when looking at the machines - you only learn this later if you need a repair and find out, "well you have the XXX-A model" carburetor.... etc.
Other than Big Box, I am limited to local brands sold. So my current choices, depending on how far away are JD, Cub Cadet, Scagg. They all appear very similar for each price step -difficult to pick a stand-out / best model. A local small engine mechanic did say the Kawasaki V-twins are the best engine. Otherwise ?
I will try to buy a high end residential / low end commercial grade in the hopes of greater long term reliability.