This has been debated a lot around here, and there's been some interesting points made about it. I have discovered that I prefer to use it at the top of the Pro Channel on instruments like rythm guitars, pads, synths, single mic choirs etc. But I prefer it a lot at the end of the Pro Channel for vocals, lead guitars, some types of lead synth lines, voice overs etc. But there's also been times when I've put it in the middle of things!
My default pro channel chain has it on top, because that's what I use the most.
This is how I like it. Experimenting is the key here.
If you want to be very authentic about it, the correct place to put it is at the top of the Pro Channel since it emulates what traditionally have been the first part of a console that the signal hits, and the sound would be processed after that. Unless, of course, you would use guitar pedals, external preamps and such before the signal hit the console pre amps. But in this day and age, you're not limited to think like this, unless you want to
I love the Console Emulator - one of the coolest things in the world!