I'm not using V4L, but I did have a similar experience. In the beginning I tried many different prefilled carts (510 and 901) to get an idea of strengths and flavors. Probably tried 20 flavors, and while the nic could be good, the flavors were never good to me. I found out later that it was not the flavors themselves, but that I didn't like PG, which is generally the vehicle in prefilled carts. Once I switched to DIY and VG-only juices, virtually all flavors are SO MUCH BETTER! More true, and much smoother...and they don't make my lungs ache and head hurt like PG did...as well as other less savory gastric results I won't go into...
Perhaps its time for a little DIY?