There is a negligible weight difference between the two, with any advantage in grams saved or gained on the hub made up with the rotor and mounting hardware. Hubs will either have a six-bolt or centre-lock mount for disc rotors. Hubs designed for gravity riding may be made from steel, where the weight penalty is worth it when balanced against catastrophic failure. Most MTB hubs are made from alloy, with some ultra-high-end options utilising carbon fibre to reduce weight. Sealed bearings are also more expensive to replace. To crack one open, you'll have to carefully peel out the waterproof seal, remove the old grease, remove the degreaser, and pack them with fresh grease before replacing the seal, being careful not to fold or damage it.
Cartridge bearings, on the other hand, see everything packaged into a sealed unit, meaning they are much easier to replace and don't require any tension adjustment, but they are a bit more difficult to service.