Both sweet potatoes and pumpkin are good for dogs health.
But when choosing between pumpkin and sweet potato as one being healthier than the other for dogs the pumpkin is more healthy for your dog than sweet potatoes.
Pumpkin is more healthy for your dog than sweet potato is because the pumpkin contains less calories than the sweet potatoes.
The Pumpkin is less likely to increase your dogs weight than sweet potatoes.
Sweet potatoes contain more calories than pumpkin and if you feed your dog too much sweet potatoes then the dog could have an increase in weight gain.
However if your dog needs to gain weight then sweet potatoes would be better for the dog to quickly gain weight.
I would recommend feeding your dog both sweet potatoes and pumpkin for the most health benefits.
Even feeding your dog some fruits and other vegetables will keep your dog healthy.