Yea you can't choose the rooms. In Ginza Club the girls basically wait in these rooms so what room you get is determined by who you're seeing.

In Ginza empire you don't really get to choose but for example when I did my back to back punt last week. They gave me the biggest rooms there which was 27.

That said most rooms are pretty good. There are some where the showers are a bit small but it's fine and most importantly they're all equipped with lots of mirrors including one on the ceiling for you to see all the action no matter the angle.