There are essentially cosmetic differences between the barreled action of a 1500 and Vanguard, but that's it. Bolt flutes, orientation of vent holes, rear cap, things like that.
However, when you buy a 1500 vs. a Vanguard, you get very different stock designs, different barrel lengths, etc. They share internals, but you might like one better than the other, depending on features and fit. Weatherby also sells some custom packages like ultralight stocks and fluted barrels, or you can order a custom build on the web if you want, with whatever features you want -- for a price, of course.
I have a Vanguard Sporter (24" blue barrel, checkered satin-finish walnut stock with rosewood cap), and it shoots really well. I'll vouch for Howa, and I like Weatherby's stock designs; they fit me perfectly. Howa action is very similar to a Remington 700 action; the same scope mounts are even used on both.
I've seen a beautiful varminter built on a Howa barreled action, with a hand-made custom extra-fancy walnut stock. Shoots like a varmint gun, but looks like a showoff sporter but with a fatter barrel.
You can buy the barreled action from Legacy Sports, along with various rifle packages, stocks, etc. Weatherby sells another bunch of different rifles, and stocks to fit the Howas also. Hogue, Boyd's, Knoxx and perhaps others sell the same stocks they sell through Legacy; AFAIK the Weatherby stocks are only available under the Weatherby name. They have some nice high-tech ultralight stocks; they're not cheap, though.
Browse around
http://www.legacysports.com and
http://www.weatherby.com