Well if JJ Abrams does an extraordinary job on episode 7, wouldn't we want him to return for the other episodes? I would. I know not all have the same optimism as I, but I have faith that he can and will deliver something great, based on his previous work and what I've seen so far for 7 (again, not all agree, just like not all agree that ESB is the best SW, except that it is). Plus having the same director helps keep a consistent style between the movies as well as having the groundwork planned out for the future releases (just as Jackson was able to do with LOTR trilogy). Anyway, imagine if Kershner returned to do ROTJ following after his successful ESB...

But, I suppose it's also fun to speculate who else can do a good SW flick - at the moment I'd cast my vote out for the Russo brothers (who both did The Winter Soldier).