First I would look for used. The deals are out there bigtime.
I bought my John Deere 4700 with low hours for a steal. The guy needed money and I grabbed it. I called the dealer the day after I got it to buy a new seat and the dealer offered me $10,000 MORE than what I paid for it to buy it outright, not even as a trade in.
As far as which brand to go for......That comes down a lot to personal preference.
I have the most hours running New Holland, John Deere, and Kubota.
I find they are all well made, great tractors.
My personal preference is John Deere in the 50hp range tractors. I just find them more comfortable to operate. I like the location of the controls. I feel more stable on them whereas I felt a little more "tippy" on the others. But that could also be just me, or the way they were set up.
The 3 tractors I ran of the brands, all were comparable specs and HP. They all had great power and I cant say much bad about any of them.
I highly recommend the next couple of Jobs you have to rent them. Spend a day on each one and then pick what you like. Thats what I did. I used to rent tractors a lot before I bought mine. Had 3 rental places and each one had a different brand. I found that after a few times, I always went to rent the Deere. So thats the one I bought