Re: bushmaster ar.
The Bushmaster XM-15 was the first AR type weapon I bought. I have had it for close to 20 years and it has fired thousands upon thousands of rounds very reliably. As far as off the shelf mil-spec AR's are concerned i think they are a good rifle.
If 700.00 is for a new one i believe thats about what Cabelas sells them for when they are on sale. I'd say go buy the thing and shoot the hell out of it. If there is something you arent particularly happy with, you can always tailor to your liking.