I mark after sandwiching. Either iron-off pounce with stencil or I pin marked paper (goldenthreads or tissue paper) to it.

I only do straight line quilting so I mark it as I go with a clover chaco liner. I have the pounce pad though, in the unlikely event that I'll brave free motion quilting.

I am a hand quilter and am now quilting a 90 x 90 quilt with cross hatching in a hoop. I didn't mark before sandwiching because I planned to use masking/painters tape. After much frustration and many tears I've discovered that it just doesn't work on large areas. I have removed almost as much stitching as I have put in because of uneven lines. I tried marking but with the batting (poly) I can't get accurate lines. So, I have vowed to mark all my tops prior to sandwiching no matter what the design is. It will certainly be faster than ripping out my stitches.

I've done both. I think it is better to do it before, but if you are using chalk or a pouncer you have to do it after it is sandwiched. I say to do it before, but I seem to be much like everyone else--I forget to, or don't have the right marking thing, or haven't figured out what to do. Most often I just free motion quilt everything. I have found if you figure out what you want to free motion in the different blocks of the quilt, practice on paper and when you are ready to quilt it is second nature.

Never before because I like to wait until it is sandwiched to decide how to quilt it. I do hand quilting and have used many different marking tools. I like the Frixxion (spelling?) pens that the marks disappear when they are ironed but come back if really cold. They are wonderful!

Be careful. Some have found that they end up with light marks on darker fabrics from the frixxion pens. Almost like a bleached out line. The fact that they come back when cold means the actual chemical that makes up the pens is on your fabric forever, and who knows what the long term effect might be.