well I'm about to find out
 

My guess is .biz will be best I just regged some for local lead gen sites. I think .us might work for some stuff. If you are trying to develop a mainstream branded site though you'd be crazy to go for anything but the .com.

You might want to avail yourself of the numerous training resources, videos, articles and audiobooks on this Internet Marketing Site

even for feeder sites .us and .biz are worthless.