I'd say it depends on how you plan to wear them. I have two POs, 43mm GMT and big Chrono and while both are good for casual style, they are a little too thick for suite. 43mm GMT is still manageable though.
But if you want one watch, the best all-arounder, it's definitely 300m for me. Have just bought two within a week time. Perfect for both casual and classic, thin and light, specially on rubber. You can't go wrong with Seamaster 300m. Also added a PO GMT for comparison. I have 7' wrist.