Man that's a loaded question. Everyone will jump in and claim "their" brand as the best due to loyalty.....obviously JD and Kubota are the two biggest brands, but I wouldn't say the best. There really is no best, it's personal preference. You could go buy another mahindra and it could be the best machine ever. Or not.
I've read countless threads about what the best machine is and again, it boils down to personal preference. Kubota and JD have the biggest market out there, and the most dealers, but that in itself in no way makes them the best.
Find a good dealer close to you is probably very important. Try out different brands. I've had Cub Cadets for years, and NEVER had a problem with them. Other people have had big problems with them, and their reputation has been tarnished by various practices. I have 3 Cub Compacts, and love em. My Cub 7532 will outperform the JD 4310 all day long, in my opinion, because I've operated them both.
Bottom line; asking what is the best mid size tractor here is is the same as which pickup should you buy.....ford/gm/dodge.......which TV.......sony/toshiba/sanyo, etc.etc.
You'll get an opinion from every brand owner. Coobie's advice is sound. Go try the different machines, list your particulars what you want the machine to do, and take your time trying/enjoying/buying.
Good luck and have fun shopping!