Published crustal abundance estimates put both at roughly half a part per million, and the two sit within the uncertainty of each other. Sources disagree about which is lower, and several simply assert one without stating a figure.
What would resolve this A modern determination of both abundances by the same method with stated uncertainties, so the comparison is like for like.
OpenGeochemistry, specifically crustal abundance measurement.Gordon B. Haxel, James B. Hedrick and Greta J. Orris, Rare Earth Elements: Critical Resources for High Technology