Program Plus has a nice old fashioned metal feel and heft, and a metal skin:
(that's mine)
I enjoy using it, 80's styling and all. I was very impressed with the viewfinder. Unlike the K100D, it meters accurately with all sorts of lenses, including the Lensbaby and a pinhole. And unlike the ZX10, it meters with the pinhole... and the shutter goes to a slower than documented speed.
If the zx10 is similar to the 5n (I think it is) then you'll need a special remote release cable, while the PP takes a traditional mechanical one.
The zx has some good points: auto focus, pop up flash, it's very comfortable and easy to carry, the batteries last, and the 5n is better than the 10.
I bought the zx some years ago when I wanted auto focus and Olympus was abandoning us SLR users, and have been happy with it. It seems well enough built, I haven't had any problems. The plastic isn't as tactile as with the K100D, but the camera is smaller and MUCH lighter.
I bought the PP last year because I wanted the A 28mm lens attached to it
but took an immediate liking to it and have used it a lot ever since. (I remember thinking: I should have bought this instead of the OM2s I did, in the mid 80s. I really like the camera!)
if you'd want a more traditional SLR then PP is great, if you want something that's more akin to the modern dSLR bodies, then the 5n is great.