Of all the resorts - getting from POR to DTD is about the shortest combo.
Our family almost always dines at Boma, so I've lots of practice at getting back from there. Much of the time, we go there directly from a park, then either use our car or take a taxi back, or head back to a park after dinner.
If you are coming from your resort, and going back to your resort after dinner, I'd probably take the car. It will be fastest, and you won't have to wait.
If you are coming from DTD, then personally, I'd PROBABLY take the bus over and take the bus/boat combo back (there MIGHT also be a bus available from DTD, like WL offers both a bus and boat. Not sure.) The boat is certainly a fun ride back.
If youa re at all pressed for time though the car may well be faster. At DTD it will depend where you park, and it's certainly possible to get lost driving around WDW. Also, someone will have to refrain from adult beverages. If it is raining or very cold though the car would be best.