First you have to actually
buy juices that have flavors. The tongue can
sense only sweet, salty, sour (tart), bitter, and umami (MSG). So fruit and
dessert juices and sweet tobaccos etc will have a sweet or sweet/tart taste on the tongue.
The rest is aroma - you need to let your nose have some fo the vapor. Ecigs do not bathe you in smell the way cigs do. You have to remember to let some vapor out of your mouth and let your nose catch it on the inhale.
Not sure which PVs have the most flavor. My weakest and coolest PV (M401) is the one with the clearest flavor. And I think many people think dripping is the method that gives the most flavor vs carts or cartos. I can't drip with M401 but use blue foam in carts and it just gives good flavor.