I enjoy going to hougang gym as it is pretty near my house. It is about 5-10mins walk from Hougang MRT station though. It can get crowded at times(6pm-7pm) and you have to wait for the treadmill :( however, it is super shiok to go during non-peak hours!!!(if you dont like crowded gyms like me) I dont go to the weights section, it is usually FILLED with bulky guys and it can be a little intimidating.
OH YES, favourtie facilities of the gym for me is the awesome bathing cubicles(water pressure is super strong) + water cooler.