Both have their advantages. 2wd is cheaper for the same HP, 4wd has more traction but will add to the cost for the same HP.
I have both and I can tell you that if it's wet out, or has been wet out, or their is an spot that is wet, the 2wd tractor will get stuck. If you have the time to deal with getting unstuck, and you don't have a limited amount of time to do what you want because it's too wet out to do anything, then getting a 2wd tractor makes sense. There are many days that I just can't use mine, and many days that I shouldn't have, but did and spent the day getting it unstuck. Nothing ruins a day like getting your tractor stuck, then trying to figure out how to get it out.
My 4wd tractor goes through just about anything. I take it out in the rain, and I use it to pull cars out of the mud who wonder off of my roads, or sometimes parked on the dirt when it was dry, but then needs to move but can't because it's too muddy. I can mow or bush hog just about any time after a rain, but usually wait for it to dry out enough not to cause ruts. The 4wd is 35hp and less then half the power of the bigger tractor. Power has nothing to do with traction.
If this is something that you plan on having for many years, it might be a good idea to consider waiting another year to save up more money for what you really want.
Having both, I will never buy another 2wd drive tractor again.
Eddie