Whichever marking method you decide on, it is always a good idea to test it on a piece of scrap fabric to see if it will remove and if it leaves a mark (some pens apparently bleach out the fabric).
I have used the pounce powder with a foam brush. It irons off without a problem but it is only visible on darker fabric. For light fabric I use the light blue wash-away pen. I just have to remember to dab the quilt lines BEFORE getting it near a heat source such as an iron.
One time I was super-smart and I used both pounce AND the blue pen. It was a real bugger getting all the blue marker washed off BEFORE ironign off the pounce. Won't do that again!
I also like the white ceramic pen for marking, as well as goldenthreads paper or tissue paper. Seal and press is supposed to be good too but I have not tried it.