I have both. The lock on the Manix tests as stronger ("MBC" rated), but the lock on the Para may be more reliable in a way since getting junk in it shouldn't affect its function. It would take pretty extraordinary circumstances to get either lock to fail. The Manix is simply a heavy-duty lockback -- a time-tested design. The compression lock is new, but very impressive. Take the time to see how it works -- I believe the stop pin would have to pull out of the liners or something along those lines for it to fail. IMO they are both great designs -- both are very ergonomic.
If you're a lefty or strongly prefer tip-up carry, the Manix is your logical choice because it's drilled for tip-up/tip-down and left/right carry.
I've never compared the thickness but I wouldn't be surprised if the Para is thinner.
I carry the Para more because it's lighter and covers all of my daily cutting needs (openning packages, cutting up cardboard, and food prep). If I were going into the woods, however, I'd definitely take the Manix.