This is in the PRO forum, and I'm not a pro. That said...
I use BHBs, sheepskin mitts, and yeah...MF mitts (all with the foamgun). I always do the first passes with the BHBs and I use the MF mitts on my best car, so if you're getting marring from the MF mitts I'd say it's technique rather than the mitt itself. But yeah, MF mitts can retain dirt so you have to take that into consideration.
Dragging abrasive [stuff] across the paint under pressure will mar it no matter what does the dragging.
I used sea sponges for ages and I've tried GS, but for the life of me I can't wash as marring-free with them as I can with my other wash media :nixweiss I can't seem to do the "dislodge and flush" thing as well, or at least that's what I suspect is going on.
Gotta admit I didn't try the GS very many times as I couldn't see any point in marring my paint in an attempt to fix something that isn't broken (ditto for ONR for regular washes). And I'll be the first to say that it can take a *lot* of washes to get the technique sorted out.
Use whatever works for *you*, but if you have to polish out wash-induced marring on a regular basis I'd say you're doing something wrong.
Here's a Q: are you folks getting much dirt in your rinse and/or wash buckets? I guess I mean especially the shampoo mix bucket, which I'd think oughta stay clean...but now that (IMO) I have my wash sorted out, even my rinse buckets stay mighty clean, even when I do a nasty-filthy wash in the winter.