I'll throw in my reccomendation for David Gym. I've been a member since November and have been very impressed. It all depends on what you are looking for in a gym, but David Gym is more focused on weightlifting than cardio. The cardio area is much smaller and features about 6 bikes, 10 treadmills and some other machines (ellipticals, rowing, etc.), but the weight area is huge and great. Basically anything you can image is there, including squat racks, Olympic lifts etc. There is also the option to try out combat sports (i.e. jiu-jitsu, MMA stuff etc. and a ton of fitness classes that range from spinning to yoga inspired classes). The price is steeper than others (ballpark about 1000 CHF for a year membership), but they have various discounts and with some health insurance plans you can claim membership at a gym.The place is really only super busy around 5-7 PM and even then you can easily work around because of built in redundancy. Also, the hours are good, from 6 AM to 10 PM weekdays and 9 AM to 6 PM on weekends. You receive 4 free fitness consults with that membership fee and the staff are generally nice, helpful and can speak English if necessary.

There are loads of huge guys in the gym, but most are gentle giants and are friendly enough. There are also lots of folks there just to get in shape or stay fit, not necessarily compete in body building championships.

If you have any questions feel free to PM me.