Methane is sort of halfway between kerosene and hydrogen. No operational space launcher has used it, though, as far as I know, some engines like the venerabe RL-10 hydrogen upper stage work horse have been modified to run on it on a test bench.
Methane is about half-way between Kerosene and Hydrogen in terms of Isp but it's far closer to Kerosene in density, which is critically important for overall achievable rocket stage performance (weight ratios). Liquid methane has about half the density of Kerosene but liquid Hydrogen has about 1/12th the density. Moreover, liquid Hydrogen is a super cryogen whereas liquid methane has a higher boiling point than LOX so handling, materials, and insulation requirements for LCH4 are comparable to LOX.
