If you go off of points per game, FC Dallas has the best record in MLS right now.
In my opinion, points per game is the most accurate way to rank clubs midseason. Right now, LA and Seattle have played 2 more games than FCD, and rankings of total points inflate those teams' standing.
Here's my favorite site for points per game:
Just click on PPG and the ranking is re-sorted.
I'm gladly eating crow, as I declared Dallas out of the Supporter's Shield race altogether when David got hurt.