Do fast moves with a higher or lower EPS number reach charge moves faster?
(i.e. Karate Chop EPS = 12.5 vs. Rock Smash EPS = 7.7 — all other factors aside — will the attack move with the lower or higher EPS number fill the charge move gauge faster?)
PVP
Firstly, PvE and PvP use different systems when it comes to damage and energy, though there is usually come correlation between them. EPS is a PvE thing, and the equivalent in PvP is EPT, or Energy Per Turn. Refer to this chart for specific move values: https://gamepress.gg/pokemongo/pvp-fast-moves
Basically though, the high the EPT, the more quickly Charge Moves will charge.
Karate Chop has an EPT of 3.5, while Rock Smash has an EPT of 2, so the former is the better charger. It’s worth bearing in mind the damage as well so, while Rock Smash technically has better damage, Karate Chop is the overall better move. Rock Smash is a pretty below average move and should be avoided.