Sourcing or sinking PLC inputs???

When i have to offer a solution to a customer what should be the criteria for selection of Sourcing OR Sinking type PLC Input modules??
The condition is that you decide on the sensors for the field , hence no compulsion for going any type.
The above would decide what type of PLC Output modules should be used.

IS there any specific standard which defines which to use in what applications (like safety etc)???

Your views would be of great help and any recommendations.

Thanks

Do a search of this site for "sinking inputs" and you will find a wide variety of conversations on the subject.

Marc

I prefer sourcing outputs and sinking inputs.

It just seems easier when testing to have 0 VDC on the input if the feild switch is open, and have 0 VDC on the device if the output is off. In terms of safety many feel that sourcing outputs are safer because a short to groung on the wiring between the device and the output will not cause the device to operate.