I agree with those who support the Jazzmaster. Jag-owners hate it when it is pointed out, but the Jaguar is like a toy by comparison.
I have a Jazzmaster (thank you, David!), and a 24" scale Squier Jagmaster (which has a Jag body and neck). I have access to a Jaguar (without owning it) and I did have a Jaguar from 1980 to 1982. The Jagmaster - with its Strat type bridge - is a fine guitar (with even more response than a Jaguar), but still not as good as a Jazzmaster.
You
can get a Warmoth neck which extends the Jaguar to a 25.5" scale length (it's a specialised replacement because the bridges are in different places on the Jg and the Jz), but... why bother?
Go for the Jazzmaster!JN
PS: loads of knowledgeable diuscussion about those two guitars (and the Mustang, Bass VI, Electric XII and all the other offset-waist guitars) at:
http://www.offsetguitars.com