mgsolakis
Don't take this axiom too far, but generally speaking, horse power is not even in the top three things to consider in a tractor. For decades, we worked our farms, plowed our long driveways out of deep snow, and did everything you can imagine with tractors such as Massey Harris Pony (11-13 hp), Ford 2N and 9N's (20 hp), little Farmalls and the like.
A tractor has grunt, torque, which is more important than sheer horsepower. Note the local lawn tractors in front of your average big box stores, all pumped up with silly HP ratings, 26 hp-28 hp, yet they are just lawn mowers, not really tractors.
A tractor must have TRACTION. It is what a TRACTor is. This comes from weight, torque, gearing, tires and the total package.
Buy what you want, but base it on lots of advice from real users. I wouldn't pay any attention to the hp rating, frankly.
and YES!!! A diesel will out torque a similar sized gas engine, drag it around the yard, and slap it up side the head!!
all on less fuel/hour usage.