The upper/lower split is the one I end up recommending to most people who ask, and the reason is boring but real: run it four days a week — two upper, two lower — and you hit everything twice (about the sweet spot for growth) with enough rest between to actually recover. It's less fiddly than a body-part split and more balanced than full-body once you're past the beginner stage.
What makes it work is the same thing that makes any split work: progressive overload and recovery. Upper/lower just makes both easy to manage — each muscle gets trained hard, then left alone for a couple of days. This builder lays out the four days around your goal and equipment and tracks your lifts. Just try it and see how it splits your week.