I am currently signed up at the Clever Fit Studio in Munich Center (5 min walking to the Hauptbahnhof and the tram Protected content 3 min walking distance).
I am looking for someone who wants to sign up for a gym :) then i can transfer you my contract and you would avoid the initial 30 euro cost that it takes to sign up (you pay this separately from the monthly fee of 24 euros)
Its cheap! 24 euros! and its never too crowded. There are weights, some classes, and also cardio machines. Most of the cardio machines even have small interactive TVs attached so you can distract yourself from your work out a little bit haha it helps me pass the time quite good.
Staff is very helpful, personal trainers available, good locker rooms and showers!