Check the viscosity of your juice. There's thin (high PG content) and there's thick (high VG content). That said, some VG juices work fine if they have added water and/or alcohol. The field test for thickness to me is to invert the bottle and watch the bubble rise. If it rises so fast it's there by the time you get the bottle inverted, it's thin and will wick well in most anything. If the bubble rises slowly, expect wicking issues as compared to PG.
For a tank or clearomizer, a mix of the two is usually good. Cartos and standard atomizers can use a mix or 100% PG or a thinned VG mix. 50/50 to 70pg/30vg is a good rule of thumb for a mix of the two. It irks me that not all vendors advertise the mix of their juices unless you ask.
The bottom line is trial and error, but that's expensive. There ought to be a standard wicking factor on each juice. I don't know how that would be universally tested and calculated for meaningful numbers, but it would be useful.