You trying to upload it to Youtube? File>Render As> I mostly render my videos as .wmv because I can put them on a DVD with ease. When you choose .wmv go down the list and look for 8 Mbps. That is a high bit rate for top quality. Then click on custom and go through the tabs to make sure that all your settings are correct.
Whenever I don't use .Wmv I use Quicktime or .mov because it compresses really good.
Either one of these settings are fine. Try some other settings out with like a 5 second video and check for what your system works better with.
Edit: You could try .avi or .mp4. They also have good results too.