The Fox has been covered, so I'll leave that one. As for the others, the most noticeable diff. is in the ASA positions. Mechanically, they all ('cept the Fox) work the same, but they're actually built a bit differently. The Puma and Bobcat (and their elder brother the Panther VTS) are built on a 2-part reciever. To cut production costs, the Thundercat (also marketed as the Alley Cat by NPS) was designed with a 1-piece reciever. One's really no better or worse than the other, the later Cats just cost less to build, so they sold them for less. Any way you cut it, they're all very well built, solid, very tunable markers.