If you want to spend the least possible time on farming, but don't mind waiting for a few days before you achieve your goal, go with trees and fruit trees. Be sure to use garden pie wich boosts your farming by 3 points. (For example, with pie, you can plant curry trees , which give better xp then orange trees). Plant willows in normal tree patches, and switch to maples after you achieve 42 (plant maples with the pie again). But if you want to speed up the process, combine trees with planting allotment crops and bushes.