I don't know any of the mowers listed but here are some general thoughts
1) go and sit in each & every one of them , get the feel
Remember you will be spending quite a few hours in each one of them so you have to be very comfortable
Ask the dealers about adjusting the handles to your arm height , check the leg length, the deck height changing mechanism.
Have a good look at the discharge chute and walk along the side as if you were a tree.
Some chutes can add 18" or more to the deck width
Some will flip up while other will tear off
Have a good look at the size of the discharge hole in the deck, bigger is better as it will resist clogging
Look at the price of service items, belts , blades , filters & TYRES , ask to see the owners manuals and note the service schedules so you can do a ball park running cost per year . Also check how many variations of blades are available, mulching, bagging, throwing low lift sand blades etc . Ignore any supposed mowing speeds, all of them are just the width of the deck multiplied by the max ground speed so while they advertise 2 acres / hr the reality will be closer to 1 acre / hour .
Look at space for junk you pick up off the lawn while mowing .
Look at how easy the parking brake is to engage & disengage , dose it fall to your hand easily ?
I loathe any sort of electronic management system because if one single switch fails then you are stuck with a dead mower, all of them are junk to cover the bum of the factory executives . ,
Check the retail price of the interlock ( or electric management ) modules, I just replaced one @ $ 480 and it failed again within a month so I spent a whole day rewiring the mower to bypass it while still retaining the basic safety features.
Keys are far better than any key pad & give you far less grief in the long run.
I replace them regularly because they are subject to weather & fail regularly .
Take the brouchures home with you then google ( name of interlock module ) failures eg Tiger Eye failures and see what pops up
Step up & down off them, some can be really awkward which is even worse after 4 hours of mowing .
ZTR's tear up the lawn so wider tyres are better than narrower ones but can get chopped up and are very expensive .
Decks with an extra high transport locked position make driving on & off trailers easier
Lift off spindle guards save hundreds of frustrating hours grabbing tools because the belt has jumped off the pulleys or some debris is stuck in there .
Check the tension arm for both the deck & hydros.
Some have square holes for breaker bars which make belt changing easy others are chop your fingers off material.
At $ 8000 you should be able to get a demo one to try out on your grass
Ask the sales person to show you how to replace both belts then ask to do it in the shop ( that will be easier than in your yard on an 80 deg day ) .
Spin off hydro filters are better than the screw in filters & get the sales person to show you how they are changed .
Remember they are looking at a commission of $ 200 or more so make them work for it .
Spartans have the best overall package, but they have just been bought out by Toro so could vanish in a couple of years along with parts specific to that mower
Donaldson type canister filters are a must ( the major difference between kawakasi FX & the FR or FS ) and one with 2 elements .
Because the engines are behind the deck, ZTR's & RER's cop a lot more dust than a tractor style mower
Check the operation of the bypass valves and try pushing the mower, again it will be easier in the showroom than on your grass and a lot of them require tools to be opened but there is no place for a tool box while other will burn your fingers / arms trying to get at them .
Basically you can ignore the specifications, they will all be so close to being the same that they become irrelevant but how the bits are put together makes the difference between the mower being a pleasure to use or a battle or wills
