I'd say TireRack - we order dozens of tires from them each year, and have had great success.
I'm on my fourth Expy and second Navigator; the best tires I've found are ContiTracs. Excellent wearability (40K miles av'g) and good wet/dry traction. I've used Scorpions, Grabbers (highly rated, but I like the Contis better - they wear like iron), Michelins and the aforementioned Conti's.
The LTX is a decent all-season tire, but, I like to use a dedicated winter tire, preferrably studded, mounted on a second set of wheels for the nasty winters we get around here on the Exp'y and Blizzaks (impressed the heck out of me, an old time "studs only" guy) on the Nav. I'm going to go with Nokians this year, since I need some new gums for the Exp'y.