Consider your effects chain and what you're actually trying to achieve.
i'll explain this with distortion and reverb.
The differences between a distorted reverb and a distortion that's being reverb hold different properties and are much different.
If you want to get reverb that has the characteristics of some kind of distortion, lets say tape. Then you'd apply a reverb unit then the tape distortion in order to get a reverb that has been recorded on to tape or is being distorted by tape.
The other way around, a distortion unit that has reverb being applied to it, is slightly different. In this case, it's as if you're taking a distorted signal and adding reverb to it.
Back to the topic.
It depends on what you want to do with your signal and how you want it to effect the processing, as i've stated before. So do you want to have a pre-eq effect, where as your EQ would shape the frequency content that the side chain is being effected? or do you want to process the signal after the channel is side chained?
in this case, you must look to your side chain channel and ask yourself if you want to effect that particular signal in a PRE or POST effect fashion.
the PRE and POST settings are also useful for sends/return, auxiliary, and buss effects (just to throw out as many names for them as possible).
Go do some research on PRE and POST signal processing and apply it to your question that you have. when you apply and experiment, you will have a better understanding.
