I've owned all three, the Millie is the only one I kept. The Para didn't fit my hand quite right and the Manix was fairly large and bulky for what you got. Excellent knife, I just don't feel it offers much compared to more streamlined knives like an Endura. Here's what I like and dislike about all three:
Millie - Amazing size / weight ratio. Very comfortable handle with plenty of room to adjust my grip. The large lock release cut-out I could do without, but the lock itself is rock solid. Very slim and carries well due to this and its lack of weight. Excellent all around knife if you can carry one this large. I'm a big fan of the contrsuction too, G10 with nested liners.
Para - I like the lock better than the Millie and it fits in the pocket better, but that's about all I like better about the Para than the Millie. The handle only fit me in the choil grip, and I really don't like to use that grip for the majority of my cutting, something this knife kind of forced on me maybe due to my hand size. If it fit my hands better I'd probably consider this the holy grail of EDC knives, but as it stands the Millie gets the nod.
Manix - It's a beast. It's one of the most secure and comfortable handles I've held. Excellent balance, great blade-shape and very beefy handle construction. The Millie just works better for me. Those thick liners on the Manix might be nice under certain extreme conditions, but day to day there's little advantadge to carrying around so much bulk and weight for me. The only time I can think of the weight coming in handy for me is when out in the woods chopping, but it's incredibly rare I ever need to chop wood with a folder. Great knife, just doesn't fit my needs as much as other knives do. Still, the handle is a great piece of work.