I typically stack delays in order of delay time. So a shorter delay before a longer delay. I don't ever use slap back, but if I did I would put it before another delay.
I am trying to hash that out. I had a M5 with the either the tape echo or analog delay set around 200ms with a couple repeats. However, long story short, I want to re-order my board.
I picked up a Zoom G3, which should probably not go last in my chain if I have one slot as the all the time delay, so I am thinking of just getting a separate delay.
I use the Pitchfactor for my other delay needs, which are usually just trippy delays. I am toying with getting a Flashback, as an analog dry-thru would probably be sweet.