I know exactly what you mean about pet shops. :/ I work in a small pet shop, and I had quite the conversation with a customer about the truth of it all. She asked me which of our cages were suitable for a Syrian, and I quite honestly told her - none of them.
Surprisingly, it's quite a good marketing technique.
Kind of like reverse psychology. I'm honest with them, so they take a liking to me and come back to the shop for advice in future. I turned two people away from fluffy bedding on Saturday. They thanked me for being honest, and said they had no idea because every other shop had only ever advised it. I feel good for helping the hammies, and I get praised by my boss because the customers like me.
It's a win-win.
But all the cages mentioned are ideal. I have a robo in a Mini Duna, and I agree that sometimes the hamster has to tell you want they want. My little one is now her happiest in that cage. When she was in a bigger bin cage, she hid all the time and didn't seem comfortable in the space. She loves the Duna, and she's really coming out of her shell.
It really depends on the hamster. Some like cosy, some like huge.