I would choose the Planet Ocean. IMO, 42mm was the perfect case dimension for that design, and the proportions of the 42mm's case, dial, hands, are perfect. There's too much dial space space on the current-generation 43.5mm PO. Plus, many find the continuous bezel ring on the 42mm preferable to the serrated bezel ring of the 43.5. These will get harder & harder to find in like-new conditions.
For the current generation SM 300: a couple show-stoppers for me are:
1) Re-shaped HE valve. The new one looks like a Reese' peanut butter cup. Much prefer the older HE shape.
2) 8800 movement's rotor noise. I'll always opt for the option with a silent rotor.