From this: http://vaperanks.com/propylene-glycol-vs-vegetable-glycerin-e-liquid-whats-the-difference/
Propylene glycol is a tasteless odorless substance, so it doesn’t alter the flavor of the e-liquid in any way.
Vegetable glycerin is a considerably thicker solution, compared to propylene glycol. On its own, VG has a slight sweet taste which also makes the e-liquid sweeter and the flavors a little difficult to detect.
Thanks @Andre! Good save!