What is the best plugin to use on wordpress to rewrite url's. I can't seem to find many. Which is the most used. the one i tried i couldn't get working.
To rewrite urls? You mean /page-title/ instead of /date/number.php? Well, you can change that in the control panel without adding any plugin...
As siflur has said, you can change the permalinks in your worpdress settings without the need for a plugin. I generally select custom structure and then insert /%postname%/ . If you want you can also use /main-keyword/%postname%/ but that is up to you.