Gary,
I haven't heard the Seduction or the Hagerman, although both get consistently fine reviews from users. Between the two, it sounds to me like the Hagerman would be easier to build -- I think I've seen some posts indicating that the Seduction involves cramming a number of parts into a fairly small, confined space.
Just to make your life more complicated, however, let me add two others to the list for your consideration:
Audio Electronic Supply (kit/diy arm of Cary) PH-1
Welborne Labs Reveille Phonostage
I have both and keeping switching back and forth because I can't decide between them (and don't have to)!
The good news is, I think you're right: whichever one you pick, you probably can't go wrong. Good luck!
Tempest Construction Pix:
http://www.audiocircle.com/index.php?action=gallery;area=browse;album=130