Trying to Decide Between Ferris 700z and Kubota z421KW

Based upon dealers in my area I have narrowed my choice for a new mower between a Ferris 700z 52" with Kawasaki engine or a Kubota z421kw 54" with Kawasaki engine.

Price: Ferris..............$5799 Kubota............$6499

Distance to Dealer: Ferris............. 10 mins Kubota........... 50 mins

Previous experience with dealer: Ferris.....Excellent Kubota.....Excellent


Some thoughts:

Best ride for back problems....
Best machine for hills (currently use Simplicity 52" ZT mower)....
Durability...
Ease of service by owner...


Any first hand information from your experience with these machines would be most appreciated.