Parker is having the better season in my opinion. He's averaging about 3 more points with better shooting percentages nearly across the board. Parker averages nearly as many assists with less turnovers than Lowry, too. I'd give Lowry the edge when it comes to defense and rebounding, but Parker is honestly the better floor general and doesn't have much more help than Lowry. But his team has the better record.
Harden is a better scorer, defender, and also a very good passer. I'm taking Harden over Lowry, too. Or Steve Nash over Lowry. Ty Lawson and Andre Miller aren't too far behind Lowry either.