I started out with the Jr. It lasted me for years, until I really started going to crops. I stuggled with the XXL/NAV question too. In the end it was DH who decided! Lol... He said he was sure I would 'grow into it' I'm really happy with it. It easily holds an album, tons of embellies in all the pockets and holders, all kinds of tools, paper cutting stuff.
I think that once you reach the point of needing an XXL or Navigator, you just need to accept that it's going to be heavy, whichever one you choose! With the XXL you probably won't have to buy another bag, and you may if you outgrow the Navigator. (This is not to say that I haven't seen plenty of scrappin' girls who come to crops with the XXL and the P3 pop-up paper thing, and one who had the XXL, Nav and 2, yes 2 P3's!!)
The other really good thing, as someone else mentioned, it's really easy to fly with (CKU!) It zips all the way shut and the zippers have locks. I believe you can get a cover for it as well that can lock/enclose it.
Hope that helps!
--heather