depends on geometry more than which steel. id prefer the 120 for cutting

myself.
s35vn has better wear resistance and edge retention, its got a decent toughness and good enough corrosion resistance...all in all its the better steel.
its also harder to sharpen. you may not need the edge retention and wear resistance....only you can decide that.
420hc the way Buck heat treats is a good enough steel for a knife. been good enough for many people for many years.
whats more important is which fits your hand and needs better. the 124 has a 2x4 block as a handle. some like it some dont. it can be sanded down to fit your hand though if your willing to do that. we could discuss all day if ya can get your hand on one youll know real quick if ya like it or not.