Since I've only had one of each MM and FM, if the grinds were the same as the ones I've had, I would choose the MM over the FM no matter the steel for the FM. The MM just has a more advanced grind. It has a nice thicker convex at the heel that progressively gets thinner to the tip. But the thing is the grinds may not be the same as these are handmade.
As for which knife I prefer, you have to understand that my preferences may be a bit different than others here. I'm not great at sharpening, so when I get a good edge on a knife I want it to last (so I value edge retention and ease of sharpening). While I appreciate a super thin behind the edge knife, I like a knife that is a bit thicker so that I can beat on it without worrying what I'm cutting. If I've got a knife in my hand, it should be able to cut through generally everything I'm prepping. I'm not one to switch knives unless I need to do something heavy (and then I pull out the ZKramer Carbon 250).
If the FM was in White, I would take a HD2 over it due to edge retention. I've never touched one, but based on my limited experience with Blue which seems to have good edge retention, in Blue I'd take the FM over the HD2 due to better grind.
I'd take the YS or MM over either.
Based on my feelings today, if I had to choose a single knife I'd take the MM over the YS. The YS is one of the best cutters I've tried, but given how I feel today (with all the other stresses in the world) it feels like I need to baby it just a touch. The MM is close in cutting, but it just feels tougher and I value that alot. I took my MM through a cooked chicken rib cage and I'd never do that with the YS. That whole difference may come down to the fact the YS is 65HRC and the MM is 62HRC. If I were doing a two gyuto combo, I'd take both in a heartbeat.