For me my favorite is D'addario XS.
However, I'll use XT, NYXL, and XL. Across my guitars I use 9-40, 9-42, 9.5-44, 10-46BT, 10.5-48, 11-49, 11-50BT. Every so often I'll get a pack of PRS strings, Optiwebs or Stringjoy. I keep a log for my string changes and a good inventory of strings on hand.