I always tell my clients they need to be able to verbally give someone the domain name quickly and easily. There should be no need for explanations - different spellings, hyphens, etc. Length isn't as big a deal, as long as it's easy to remember.
.net is okay - I would shy away from .biz, it doesn't carry the credibility yet.
.net is okay - I would shy away from .biz, it doesn't carry the credibility yet.