synthetic oil

years ago i used Amzoil in a warm 340 Duster that i have since sold.It was pricy and i soon went back to Dino oil.
5W30 Penzoil in all my vehicles.
I had the new pennzoil synthetyic in it , got the pan off, everything looks great, but the magnetic drain plug had more sludgy looking stuff than ever before.
Wiped it off w/ fingers , nothing there , but did stick to the magnet . Think I`ll go amsoil --