Extremely convenient location for concerts/events at Hans-Martin-Schleyer-Halle.
The accommodation is clean and spacious enough for 3. Service is very friendly, and the breakfast was delicious.
Only downside is that you can only pay by card, and they had problems with the terminal when I tried to pay for breakfast. But it all worked out in the end.
Major plus: breakfast is free for children.
Downside, depending on the reason of your stay: not many restaurants around for dinner, but we ate at the Halle so for us it wasn't a problem.
Walking distance from the Bad Cannstatt train Station.
The gym is minuscule.