Is it wise to choose .xx domains?

If you are planning to buy a domain, the first thing you have to look into is to buy a .com domain. This is mainly because, .com domains rank very well in the top of google. It gives an edge to rank the domains when compared with the other extensions.
If you are unable to find a .com domain then you can go for .net or .org domains. As these domains too rank well on the top of the search engines. If your business is focused in a particular country then you can go for a region specific domains viz.. .us, .in, .fr etc.    . info domains names are cheap, and also rank well in google.
Also if you are looking to buy a xx domain name such .cc .co etc, then you got see whether you can rank them in search engines. As far as i searched, none of the domain names haven't been ranked on top of google. How often do you see a domain with xx extension ranked on top of google..
So if you are looking to buy a domain name, do go for a .com extension, else .net or .org. If you still unable to find it, then use dashes between keywords, such as keyword-keyword(.)com