I would go with the SMP300, but that's because the heritage violates two of my fundamental principles with its PCLs and lack of ceramic bezel.
That said, PERSONALLY, I don't care for the white dial SMP300, or to be honest the SMP300 in general. I wanted to love the watch, I really did. I love the bezel, the wave pattern, the glossy dial and the way it shines. I wanted to stop hating the bracelet and its lack of taper. I went to the Omega boutique to play with a couple of models. The SA showed me the white dial, and I thought it looked and felt cheap. The blue was intriguing, but still more of a novelty. The black could be a very doable daily. But in the end, I couldn't stand that new bracelet and how light (and ugly) it was.
And then the SA handed me a PO8900. Talk about night and day. It fit me like a glove, hit every right note and just felt right. Heavier, manlier, gorgeous under the light. No problems at all on my 7" wrist. I knew right there it would be my next watch, but my issue was that I'd just paid for my wife's Rolex and was on the waitlist for my 126610ln and promised it would arrive within the next six months, so I wasn't in the position to drop that kind of cash.
Don't get me wrong, because I know myself and I'm still in the market for a nice blue diver--I'll most likely end up purchasing a SMP300 at some point in the future and just forcing myself to tolerate the bracelet. But do yourself a favor and try on the PO before making a decision. If your wrist can pull it off, it's just far and away a better watch than the SMP.