I lean toward this one, too, but Google has no particular bias against dynamic pages. SEOs use to warn against using "dynamic" URLs, because they tended to include a lot of parameters and create duplicate content, but there's plenty of evidence that ".php" pages are perfectly fine.

To me, it boils down to:

(1) As TraxNYC said, all else being equal, shorter is better

(2) It looks a bit friendlier to search visitors (and easier to read)

(3) It doesn't instantly reveal your underlying platform (and pose a security risk)