It all depends on what you want to do with the buggy. If your a serious racer I'd suggest a well known brand that has good parts support. Like AE,Losi,OFNA,Mugen,and Kyosho. They all offer a great well balanced car. If your more into bashing or running out in front of your home, try a rtr kit. All these companies and a few more offer these types of kits. They all have there pros and cons and imo, these are some:
AE:Good buggy, great part support, 1st series of car, needs some bugs worked out.
Losi:Good buggy, good part support, have heard it can be difficult to drive for beginners, don't know for sure.
OFNA:Easy to drive, good part support, some circles say a inferior product, ie: parts tend to break more easily than other companies.
Mugen: Great all around buggy, drives good, part support at times may be difficult, all hobby shops are different.
Kyosho: Great car, drives great, part support is subpar in most hobbyshops, and parts tend to be more expensive than others.
These are just 5 brands that came to mind, some will agree with what I said and some will disagree. I've been in the hobby for 16 years and have owned at some point each one of these brands. To say which one is best is unfair, if we knew that, than everyone would own one. Hope this helps and good luck!!