Beaulieu if we go by the classical definition of "skating". His stride is effortless and he's deceptively quick as well. He has the Karlsson/Keith/Campbell type of skating.
Subban is more unique, though. Beaulieu is probably faster, but Subban has a more powerful stride. Once he gets going, he's an unstoppable bull on skates. We saw him overpower Lucic, of all people, quite a few times this series. Add to that he's a very agile guy despite his bulky 220 pounds 6 feet frame and the fact he's an ace at puck possession and I think overall, Subban takes it. He isn't nearly as pretty of a skater, but he's more effective, in my opinion. And Subban, while perhaps not as strong, was a lot more speedy early in his career when he was closer to 200 pounds
In fact, I'd like PK to shed some weight next off-season. As strong as he has become, I feel like 220 pounds is overkill for a guy of his frame, and it has affected his speed and endurance a bunch from my viewings. He'd be better off at 205 - 210, but heh, he's pretty good at 220 as well...