Wideband readings. Where to mount

My question concerns using a wideband. I understand how they operate, however my question is in regards to where you typically take readings from. Are you typically mounting the wideband sensor before the catalytic converter or are you taking the readings coming out of the end of the tail pipe? Is one way better than the other? I have seen a couple of times that I have had no place to mount a wide band before the converter because of piping location etc etc.

Thanks

Andre has suggested previously that it is well worth the time installing an O2 sensor bung in the collector or the turbo dump pipe. The response is much faster, and it enables you to do light load tuning without the ambient atmosphere contaminating the reading - which happens when you use a tailpipe mounted sensor.

Thanks for the response Matt. I'd love to install the wideband in the collector however it's not always feasible which is the case on the current vehicle I'm tuning...a 2007 Ford Expedition. There is no room in install an O2 bung before the collector at all.. Been there tried that, there's literally no room. I'll tune off the tail pipe mounted sensor for WOT and do what I can for light load.

Often we are forced to mount the sensor where there is physically room to do so. There's a lot of conflicting info regarding the sensor location regarding pre or post cat - the reality is that in my experience it makes little difference. Mounting the sensor in the tailpipe with a tailpipe kit is ok for high load/high rpm operation but at cruise and low rpm you're likely to have the sensor reading affected by ambient oxygen which ruins the readings.