The PM2 is going to cut better, have better build quality, and have a better steel for typical knife use. Some might also appreciate that it's made in the US and has better aftermarket support.
Full disclosure: I generally love Spyderco knives and don't see any appeal in the AD 20.5.
Cuts better probably yes. The blade shape/design is for slicing.
Have better build quality no sorry not a chance. Unfortunately the AD20.5 is another testament to exceptional foreign build quality.
A better steel maybe (PMs have been made in quite a few different steels) but the Demko AD20.5 in 3V and yes even D2 is no slouch.
Made in the US unfortunately the AD20.5 is not. I wonder if a US company would even tool up and offer the quality control needed for a brand new design and if so would it be priced out of the market. The huge mega factories in Taiwan will make anything you want if you pay for it. That is too bad. I wish the US could offer that but it's an unfortunate fact that we are not in a position to.
Better aftermarket support I would not choose one over the other. The AD20.5 has good amount of aftermarket support both by Demko (Springs, Scales, ti and stainless barrel spacers, even $10.00 white grivory scales) and other vendors who sell scales and ceramic bearing such as skiff. Paramilitary has been around and has a lot of aftermarket support.
The Demko Shark lock is MUCH STRONGER, easier to use, and better in my opinion. The action on an AD20.5 is much smoother. This requires very high precision. The AD20.5 is MUCH MORE FUN to play with. Although the Demko has no where near the ergos of a Spyderco it is still in most cases more than good enough to get most jobs done. Overall aside from the lock the Demko is a knife that leans toward the strong side.
I don't know why you didn't mention the obvious where Spyderco usually blows all the others out of the water and that is ergonomics. The is no question in my mind that the typical Spyderco ergonomics of the Paramilitary is head and shoulders above the old fashion traditional shape of the Demko AD20.5
As a user in most cases whether one likes the looks of a Spyderco or not he/she may very well have to admit that they would rather be holding and perhaps carrying a Spyderco such as the Paramilitary all day rather than a heavier and/or traditionally shaped knife like an AD20.5. Blade design on a lot of Spyderco knives will make frequent cutting less of a chore too.