There isn't a best for everyone but there is a best choice for your application.What brand do you see more at the track?What brand is cheaper to mantain and parts are easy to come by?I have a RRR because it's the most supported brand here.Xray it's expensive to mantain (at least here) and Serpent is making an effort to be well supported so if I had to make a choice for a next chassis it would be the 733.That's my option,you can make yours after thinking about wich is the best for you.
Oh and about Edam,HK-1 and such,they're underdogs so keep an eye on them also.
Check out this URLs for setup help/debate - www.rctech.net/forum/tags/spreadsheet.html
Brands I like - HephaestusRC, Robitronic, Kyosho, LM Engines, Mugen Seiki, Graupner
My home track -> www.rctech.net/forum/racing-forum/775876-crmpl-off-road-track.html