I live in KW and have played at all the places mentioned above.
Let me try to give my honest high/lows of each location:
KW Badminton Club:
mostly younger players, the older players are very skilled
highs: good calibre play, 24x7 access, dedicated badminton courts/lighting
lows: when I played there, people were snobby, tend to play in groups (except for ladder nights), place was REAL cold in the winter (haven't played since they put up the insulation though), and although not stated, pretty much feather only, used to be really expensive too, though I understand that has changed
Breithaupt
Somewhat mixed with more older players
highs: cheap, mostly beginner to intermediate, friendly atmosphere
lows: concrete floors (really feel it on the knees), low ceilings (watch those clears)
Forest Heights
Crowd is predominantly older
highs: cheap, friendly people, real gym (regulation ceiling and wooden floors), mostly beginner and intermediate, with a handful of good players
lows: can be busy
UW badminton club
All UW students from 1st years to post grad
highs: cheap, modern facilities, lots of courts, wide variety of players from beginners to almost varsity
lows: BUSY, must be UW/Campus rec member, stingy with birds
Hope that helps...