Pickaxe is the exception yes, because it has the Great Axe moveset. But no, all Great Hammers swing the same speed but albeit some have increased stamina consumption on swings (an example would be Great Club vs Ledos for stamina drain. For most weapon classes? Yes. They all share the same moveset minus some in the Halberd class (see Gundyrs Halberd swing vs Red Hilted Halberd) or the Greatsword class (see Hollowslayer swing vs Claymore; Hollowslayer is faster) some exceptions like that come into account. Other than that they all swing the same, the only thing they don't share is AR, reach, and most of the R2s.
IMO I still think Great Club is the best hammer. For PvP and PvE. I've never tried Ledos in PvE but in PvP, it's very good.