I've been carrying a Spyderco Tenacious for 4 or so years now, my Christmas Present to myself was a SpyderCo Paramilitary II.

I have a couple of observations.

First, I chose this knife because the Mannix 2 was out of stock.

I like the G-10 handle of the Tenacious.
I like a hefty knife.
I wanted better steel than the Tenacious. While my Tenacious is still pretty sharp, the edge rolled a little and it's not where it was. It's also serrated so sharpening is difficult and beyond my meager sharpening skills. I can do chainsaw chains but my knife sharpening skills blow.

The Paramilitary II is lighter than the Tenacious. I personally consider this a negative although it's only a little lighter.
The stippling and grip on the PMII is much better. The Tenacious is almost slippery comparatively.
The blade on the PMII is sharp as fuck from the factory. It's exactly what you'd expect.
The open is exactly the same as the Tenacious. I can flick the knife open rapidly with either hand.
I can close the Tenacious with one hand, the PM requires two hands, at least for now since it's a back lock. No biggie.

While I'm happy with this knife, what I really wanted was a Tenacious with better steel, which is what I think the Mannix 2 is. That said, this one will go in the pocket for EDC and the Tenacious will be the weekend warrior and get all the shit jobs that really fuck up a knife.

As far as Value goes, the Tenacious really is a great value, probably the best-in-value folder you can buy.