Those descriptions are somewhat contradictory. I think low clamp implies top swing, and high clamp implies bottom swing, but everyone seems to use different terminology, so who knows. This link gives a pretty good summary of the two major types:

http://www.bikeman.com/bicycle-repai...derailleur-101

You may also see different variants designed for different chainstay angles as well as top or bottom cable pull, though most FDs these days are "bi-puller", as someone already mentioned.

Since you already tried a Tiagra FD, and it fit on the seat tube and didn't overlap any bottle cage bosses, I would say trying the more traditional high-clamp style first is a reasonable guess. I had to go with a low-clamp design on my last build (involving a Nashbar touring frame) because my old FD's clamp ended up right on top of a bottle cage boss.