IMO, 9 speed chains from Shimano, SRAM or KMC should be equally durable. It's pretty unusual for a chain to break while just riding along, even with a big load. Usually the chain has been previously compromised by chainsuck or some other mishap. Also chains can break if improperly connected. For your 9 speed and higher they should only be connected with a quick link or Shimano pin. Don't try the old method of pushing an existing pin back in.