I have a pair of Millies (old serrated 440V and plain edge S30V) and a pair of identical plain edge D2 BM710s.
I have to say it's a hard choice. I would have said 710, but I recently got to cut some 1-2" roots in the back yard with the serrated military, and the handle shape (pommel shape specifically) and the longer handle and the big hole for opening while wearing gloves all worked so very well. I was a little concerned about accidentally disengaging the lock, but I wore heavy gloves and the knife hasn't been sharpened after a rozen hard roots, so I thought what the heck and kept sawing completely ignoring the lock, and the lock didn't even move.
I'm not sure I could repeat that with the 710, the pommel on the knife wouldn't prevent the hand from slipping that much, my knuckles would bump into the root (where with Military's longer handle my hand was on the back 2/3 of the handle, away from what I'm cutting) and the slightly bent shape of Millie's handle allows to bring more forward pressure, and thumb resting on the thumb rest with notches on it I could put all my weight into a cut.
In short, 710 is a very classy knife you can carry anywhere, and it will perform any task very well. But if you want brutal cutting power and extremely secure handle that would prevent your hand from sliding onto the blade or your hand off of the pommel, I'd go with the Military. But Military WILL raise eyebrows, especially a serrated one, whereas 710 looks a little too urbane to really scream "WEAPON!", I don't know if that's a concern or not.
About the ease of opening, I would go with Military again. That BIG HUGE opening hole is very hard to miss, with the round cutout on the front scale your finger will end up there all by itself, then spin, and it's open and locked. With 710 I might have issues upening it really fast, you have to find that stud first, and it offers a lot less purchase than the hole. For closing, Millie is just a liner lock, press it with your thumb, push the blade spine with your index, pull your thumb out, close the blade. With 710 I just close it on my leg pushing on the spine and thumb disengaging the lock. So one-handed opening and closing is easy enough with either one, but when it comes to depoyment speed, I'd go with Millie, it has the biggest hole, can't miss it, and now that they don't bevel the hole edges, your finger is unlikely to slip out once it's in there.
It's funny, really. A few weeks ago I'd have said 710 and have no doubt in my mind. Mind you, I do carry the 710 and not the Millie when I go out, but Millie is waiting for me at home, and deals with all the nastiness in the yard. I'm actually thinking about getting a new serrated Millie, the old one is almost toothless after so much work.