3.55 is the way to go. If you are on 3.50, update to 3.55 OFW and then install 3.55 CFW.
There is nothing higher than 3.55 CFW. (3.56 doesn't count because its horsesh!t).
The best CFW available at the moment is rogero CFW v3.4 (which is based on 3.55) IMHO. Kmeaw is stable and basic, Rebug is stable and full of options (half of which you will never touch), and rogero really is an updated/newer fw than KMEAW with more features.
You can read about CFW's: http://www.ps3devwiki.com/wiki/Main_Page
You can download OFW/CFW from here: http://www.ps3devwiki.com/files/firmware/