The H2S is the workhorse of the H series: full engineering capability with one nozzle plus AMS 2 Pro. The H2C swaps between six hotends plus one fixed automatically, so multi-material jobs skip purge towers and cross-contamination entirely. Volumes are close (340 x 320 x 340 vs 305 x 320 x 325 mm; the H2C actually gives up some X-width to the tool changer).
If your multi-material need is color, the H2S with AMS does it cheaper. If it is functionally different materials in one part, rigid plus flexible plus soluble, the H2C is the only Bambu built for that.