I've owned both, loved 'em both too, but if it were me I would choose the Millie. Here's why:
It's very light and carries high in the pocket, which makes it conveniently accessed. It's not an issue to me since I live in a small town where you'd have to stalk around with a broadsword before anyone even took a second glance. In the city where people are more prone to get excitable regarding the mere presence of a blade, I'd say the SERE cuz it rides nice and deeply. The SERE would also be slightly preferred hypothetically if you do alot of vigorous activity, or walk in alot of tight brush, since it makes it harder for the knife to sneak out.
The SERE is built stoutly, but in places I don't care about. sure, it has thick strong liners, but I rarely abuse the liners of a knife. It's tip is slightly strong than the Millies, but not enough to make me forget that sweet handling flat ground blade on the Millie. The S30V on current Millies is pretty sweet too. Not that there's anything wrong with VG-10, it's damn good stuff too, but given my druthers I'd take the S30V.
I like the handles on the Millie much better, which is once again a matter of preference. I have very thick forepaws, and badly damaged wrists and shoulders- Smaller handles don't do well for me with extended use.
I prefer the large opening hole on the Spydie- mainly cuz in my location half the time my hands are gloved, and the other half they're numb, during the winter. In the summer they still wind up numb half the time and get their fair share of blood and sweat on 'em.
I own very few knives, and tend to wring every bit of versatility out of what I do own. I've found the Millie to simply have a more versatile blade design than the SERE.
I like the SERE very well. it is incredibly smooth, compact and a very sharp little blade. It also tends to have a liner lock you can trust more than most, but for my money I'd still go with the Millie first, but that's just for my lifestyle, enviroment, budget, and physical build.
IT'S AWSOME !!
