Keep most the weight on the rears through proper ballasting and a 4wd has little advantage over 2wd. Some task make it impossible to keep the weight on the rears - like heavy front end loader work. So for some uses, 4wd truly is the way to go. But if you have no loader and are doing everything with the rear of the tractor, get the biggest 2wd you can get for the money you want to spend, fill the rears and add wheel weights if you can as well. Keep an implement or weight on the 3pt if it's hilly make sure the heavy end of the tractor is pointed up hill going up and down. It's amazing how much 2wd gear tractor you can get for the price of a smaller 4wd hydro and the 2wd makes sense in some circumstances.
All our family tractors that did not have loaders were 2WD and never had traction problems as long as the tires were good. They were great for mowing, brush hogging, plowing fields, disking etc but NOT snow plowing. We had one 2WD with a loader which was worthless with weight in the bucket. All the others with loaders were 4WD.