Generally I would say that planetary gear motors in each wheel hub is the most stable and less complicated solution in a wheeled RC construction vehicle. Fumotec useds that solution for scale 1/14, with MFA gearmotors diameter 32mm. When it comes to scale 1/8 I don't know about similar gear motors that are strong enough to put directly on the wheels, (10-12 inch diameter?) So a better solution is the diff. option I would guess. But if thinking of diffs from like 1/10 - 1/5 RC cars, they would need being connected to a planetary gearbox in the wheel hubs, to be able to transfer the torque needed on those large wheels. Possible the easiest solution is building the whole gearbox/diff/axle set-up from scratch, using more heavy duty gears than comes with any RC car. Then one can possible just forget about planetary gears in wheel hubs, using a solid shaft and large tooted gears in the diff/gearbox. Would possible consider a large brushless motor, of like 500W ++. Another option is using 4 separate gear motors (MFA 32mm planetary gearbox with retrofitted brushless motors for more power, not in each hubs, but 'on-board' the body of the shovel, each connected via shafts/universial joints to a pair of separate bevel gears (like for angle grinders, about 1:3, cheap on ebay) where the diffs. normally are located, leading on to one wheel each...If you can imagine what I mean
Then one don't need thinking about making diffs..