In our current format, Porygon 2 is better than Claydol.
The more supporters, the better. That's the bottom line. Power Spray kills Uxie and Claydol, and often people find themselves stuck with no supporters. At least if you're playing the Soviet Engine then you will often be able to ensure that you get a supporter drop every turn. And it allows you to play a disruptive supporter like Lookers, while allowing you to use another supporter to help you,
Uxie has the same problem late game, unless you run the X. They're obviously a one time thing once you lay them down, and you remove them with Lost Cyclone so you'll never be able to use them again.
Don't get me wrong, I still think Uxie is the best choice because it fits more in with the all basics theme, but Porygon carries the advantage of relying more on supporters than on powers, which is better for the mirror.