Other than just test driving the tractors, seems your about as prepared as your gonna be, brand on this one is kinda irrelevant, some have Luck with brands and models and some don't. There's no one brand that stands out as a brand to look out for.
Things to look at when sitting on the tractor is layout of the machine, do you have to by a gymnast to hit the directional pedal and deff lock at the same time?
How comfortable and easy to reach are the FEL controls if your buying a FEL.
How easy are fuel and oil filters to get to if you plan to do maintenance yourself.
For a tractor with duel rear brakes, deff lock and directional HST pedals, John Deere has the ideal layout, some tractors are almost impossible to use without doing 10 months of yoga classes first.
With a 1 or 2 series tractor your not likely to find duel rear breaks.
My dads 445 is break up high on the right side, separate directional pedals for your toes on the right, and deff lock for your toes on the left.
My tractor is seperate directional HST pedals for your right toes, left heal is deff lock, right toes are duel brakes which makes operating duel brakes and the directional HST pedals easy.
My mower is HST forward and reverse on the right fender and brakes on the left foot.
There all a little diff but for example if you have your brakes on your right foot like the JD garden tractors and your trying to lock one rear wheel for a fast turn, you would have to have your right foot on the directional pedal and your left foot on the right side of the tractor operating the duel brakes, puts you in a very awkward position.