Both deadhead towns (technically cities as you rightly say). They've spent a bit of money on regenerating Donny, with the wool market development etc, some good eateries in there and within the proximity. However, it is a traveller town which brings its own issues, like with nearby Barnsley. Always cause trouble at the boxing shows I attend around there, the drink is usually the common denominator.
I have visited Doncaster a few times to go out for dinner, it's one of those typical Yorkshire drinking towns, so even the places that have had a facelift are full of the bootcut jeans wearing fellas and fishwives in tow, we've had a shit time each time we've been, space invading mouth breathers all over you in the bars and restaurants. No facelift will ever breed any class into areas like that, unfortunately.
I used to have a few building sites I helped manage in Rotherham, the purple hair brigade with loads of kids not in school was par for the course there. Seen one you've seen them all. Each development was forever being vandalised and tools nicked if they weren't nailed down. The type of place where someone will take a workman's trowel into the pub and try to flog it.