It's hard to compare these two. Not because of graphics or GUI or what not, but because they are not the same really, like SQ or KQ.They are both amazing games.
I was a fan of King Arthur before I was even born.
Graphics are equally spectacular to me. Camelot because that is only 16 colors man! And Longbow, because I'm a sucker for VGA.
Camelot had involving instances like the riddle stones, or jousting against the Black Knight.
Longbow had choices and suspense.
Finally, one cannot forget the mushy love stories.
The sadness of Arthur, his knowing of Lancelot and Guinevere; and Robin saving the damsel in distress. WOOT!