Lots of advice for flavors to try but as we all know here, what one person raves about the next may find disgusting. Funny how our taste buds can be so different from each other. Your best bet is to go with 10ml bottles or smaller samples. I think some vendors offer 1 or 3 ml sample bottles.
I guess I'll be the first to ask, what hardware are you using? Battery device, carto etc? Are the cartos single or dual coil and what ohm rating. How are you filling the cartos? They can be tricky, looking saturated on top but too dry near the bottom where the coil is.
Every combination of battery and delivery device, whether it be a carto, clearo, tank etc has it's own sweet spot where it produces it's optimal vape. With no winners out of 15 flavors, maybe some attention to your hardware would yield some benefits?