It sounds like you are far from a newcomer to Tractors. The advice about the dealer should be old news to you, and I presume you have some familiarity with your Case dealer, who may be the same guy as the Massey dealer. For me, the Case guy also sells Cub Cadet and Kubota. The Agco (Massey twin) dealer also sells McCormick. The NH dealer also sells Massey and Deutz.
The common advice for CUT buyers is to run 'em all for a while. Sit in the cab, try out the fit of the controls, the comfort of the seat, the workings of the pedals, etc. Run the loader up and down some, check the ease of access for service and maintainance items. See how easy it is to hook up to a big implement, watch the loader, take the loader off, etc. Play with the things a while.
You're planning to spend a lot of money, so the dealer should be willing to spend a lot of time helping you decide. Ask them why one is better than the other, what kind of service history each has, which they like the best and why, and so on. Remember the NH line is essentially a mechanical twin to the Case line, but you might like the looks of blue better than red. Lastly, see who will give you the best bottom line deal, including "free" hats, shirts, 50 hour service, delivery, pick-up, tire loading, or what have you. Take your time before you let them take your money. One of the tractors will eventually kind of work its way into your head, and that's the one you should get. For me it was the Case DX29, despite the fact that I started out looking for a Kubota about 3/4 that size, looked at Deere, Mahindra, Agco, Kioti, TYM, Cadet, Massey, and New Holland. The seat, the telescoping rear links, the lack of lines and filters and such hanging down below the tractor, etc. just made me think that it was a pretty good machine. The Mahindra looked good until I compared the loaders and buckets, where the Case just beat the snot out of the red machines from India.
Good luck with your choice.