At first I reacted with the Mets don't even have the best rotation in their own division, but thinking about it - it's an interesting debate. The Mets may have the best 4/5 in their rotation but overall who do you pick as the best?
Astros - Cole, Verlander, Grienke, Miley, Sanchez
Nationals - Scherzer, Strasburg, Corbin, Sanchez, Hellickson/Fedde
Dodgers - Kershaw, Ryu, Buehler, Maeda, Hill/Stripling
Mets - deGrom, Syndergaard, Stroman, Wheeler, Matz/Vargas
Teams like the Twins, Rays, and Cleveland are a level below those 4 teams IMO.