Because US corporations didn't think American audiences could take Japanese, they tried to use the hip langauge of 'x' included in the title. Thinking they were brillant because of the X scar on Kenshin's face. Instead, its one of the biggest jokes of the 90's.
LOL... indeed, just to call the series samurai X because of the scar in his face is lame. There's a deeper meaning to that scar than just an X, or a battle wound! But as mentioned before, there's no difference between them
samurai X explains about the orgin of how kenshin got that scar. that's all. there isn't a different, as it just focuses on how kenshin was younger in the past.
i believe samruai x, especially the first ova's to be more entertaining than the actually series. It has more present themes and the battle scenes are better animated and more vivid.