"When I wants whiskey I drinks whiskey and when I wants water I drink water."
If you want a weapon that mounts on your long arm I would go with the M7.
If you want a wire cutter/saw/bottle opener that fits on your rifle then go with the M9.
I voted M7.
So you have not discovered the old "Stoner 63" bayonets? They had the wire cutting feature and the saw on a much lighter blade that was abit thin for my taste but where lighter than the M9. Some "63's had a storage space in the handle, some had a front sight tool in the handle and some had solid butt caps with no sliding door at all. I suspect Stoner got a look at an AKM bayonet and thought "why not?" They fit the M-16 series rifles as well as the Stoner 63 and they fit the AR-18/180......he wait Stoner had something to do with all those!
I did a review of the Probuis Bayonet right as it was adopted and played up the many uses of the M9 bayonet but honestly, for use as a bayonet the M7 would be my choice. In my first old Infantry squad we all carried one or more small tools, one guy a set of vise grips, another a hacksaw blade holder and blade, another decent wire cutters, I carried a Cresent wrench and sharpening stones and another carried a double ended screw driver. At least one guy had a TL59 linemans kit of that black handled pocket knife with a single blade and a "tool" blade that had an edge but ended in a flathead screw driver and this in a pouch that held a set of lineman's plyers. No it was not convienient to have tools scattered so one had to find the right guy to find the right gear.....but dedicated tools worked better than an M9 could.
As a kid I carried an M5A1 bayonet as a sheath knife most of the time and an M4 bayonet for most of the rest of the time. I never found them particularly lacking as a sheath knife. As a bayonet I really liked that blade shape and style if it were sharpened on both sides and country to what some have written in our other bayonet discussions in my Infantry unit all were kept sharp including the short top "false edge".
If I wanted a bunch of tools in a handy package then my pocket knife would be a Swiss Army knife and I would have a bayonet that was good at being a bayonet.
-kBob