I usually go for sales, not a specific item...
GreatModels has the best 'regular" prices CONUS and now you can FINALLY tell if the item is IN STOCK before you purchase!
Squadron - huge selection, high prices unless you go for their "green" sales (good deals)
LuckyModel - Some of the best prices, if you can figure out their byzantine shipping calculations and are willing to wait 2 months for your kit. On the other hand, their small selection of AM offerings are cheap and free air shipping. Go figure
SprueBrothers - good reputation, medium selection, fast shipping, better prices than squadron
E-hobbyland - small selection but great prices.
For naval stuff, cutting edge, new releases, hard to find items... dont forget the japanese stores, HobbyLink Japan and HobbyWorld Japan... sometimes they DO have the best non-sale price for a specific item, even including shipping