That's a hard question to answer without some additional info from you. What is your price range? Do you want a static prop or one that lights up? Do you want one with all the bells and whistles (lights, sounds, special effects, force motor, etc)? Do you want one from a movie or a custom design? Do you want stock off the self, or do you want a custom? Can you do the custom work yourself? Would you need a sabersmith to do the work?
So, obviously asking which one is the best can't really be answered easily. I think you might want one that lights up and makes sound. I would grab one of the newer Hasbro FX Sabers or an older MR FX Saber. These are in the $120 range and are very nice. Do some research over on FX-Sabers.com. That's the best place to be for saber related questions but of course many people here can help as well.