Gah! You make me choose?! Fine then. Cookie first...
Vikings, like Delfos said, lived 1000+ years later, thus giving them a technological advantage. Plus, though the phlanx was the best infantry tactic of its time, it only had to deal with archers, spears, swords, and the occasional chariot. Because of the time change, now have to deal with more advanced forms of the same group of weapons. Pikes, longer swords, heavily armoured cavalry, war axes, and advances in bow craftsmanship and technology. Spartans lived during the Bronze age, giving them weapons of great quality, but when compared to the refined iron weapons of the Vikings, there would be no contest.
Again, Spartans made up the best infantry of the Greeks, they weren't renowned for their naval power. Though the Greeks were a great naval power, more so were the Vikings. The Greeks had their triremes, which could only go up to 6 knots with 300 rowers. The Viking longboat was much more agile, allowing them to conduct surprise raids anywhere.
So Vikings win, hands down. OWNED, my friend.