Whats better for.... what? Each has different properties, benefits, disadvantages in your mix. Yes you can use both.
PG keeps the flavor better, but makes less vapor.
VG makes more vapor, but seems to suck up flavor.
Glycerin is available at rite-aid, walmart, duane reed, whatever - you want USP. PG is available online, at tack shops, at tractor supply stores, and can be ordered
through your pharmacy. Again, you want USP grade.