"Best e-Juice" is highly subjective, sort of like asking what is the best dish at the best restaurant would be. Would be more informative if people could post a more descriptive reasoning behind their choice of "best" juice.
For myself, my vendor of choice is VapingUSA.com
My top picks in flavor there is green apple, grape, watermelon (actually, it tastes like a melona bar) and strawberry all at 100% VG, 6% nicotine. I just order two 30ml bottles now, one with 12% and the other at 0% and just put them together since 12% and 0% is the lowest option.
Most of all their juices come in clear liquid, not much, if any dye seem to be used here. I like their line because there is no chemical or soapy aftertaste, flavoring is on the milder side too. The best way I can describe the vapor taste is "very clean." Liquids have great aroma and produces lots of vapor. Most importantly, their e-liquids DO NOT react with any plastic/polycarbonate tanks.
Spearmint is also another flavor I like, but I use more as a topper/additive to give some of the other flavors a bit of a sweet minty flavor. The color of spearmint is more on the lighter yellow tint, similar to strawberry.
Peppermint has a stronger, sharper mint flavor, sort of like an altoid, but not sweet like the spearmint. Liquid is clear.
Vaping straight spearmint or peppermint is way to strong for my taste, probably ideal if you were a former Newport or Kool smoker, I think it would blend very well with their tobacco line.