I went Aldor because I would rather get a chunk of dodge when my SSO pendant of resolve procs instead of a chunk of expertise. The Aldor shoulder glyph is nice for Prot, (and you can always get the Prot head glyph from Keepers of Time), and if you can't get the Jade-Skull Breastplate to drop in Mechanar, the Chest that you can buy at Aldor revered is superb for Prot.
Of course, it IS easier to get Scryer rep, and their stuff isn't bad either for tanks, I just happen to prefer Aldor.
Not sure if this will even matter much once WOTLK hits unless the Aldor/Scryer vendors get some level 80 stuff....