It doesn't really matter what extension you have (except .ws and .cc, hehe) if you have a top fold dictionary word domain name (these sometimes can go for thousands of dollars on eBay, perhaps more depending on the name).
Otherwise, your best bet lies in the .com and the .net.
Try to limit your abbreviations, and arcane words, and try to make the domain catchy / easy to remember. Ask yourself, if I was a ______, would I want this domain? (insert whatever industry occupation your domain is relative to)
Mix and match words, sometimes they make sense, sometimes they don't...
Yay:
webhosting.com
Yay:
hostingweb.com
Eww:
sitewebhosting.com
Eww:
webshostings.com