I would say for both,because Arthur said that he would never trust Gwen again and there must be TRUST between two lovers.

But I feel so sorry for Lancelot (and it seems that noone cares about him,but they only want Arthur to learn the truth,so he'll trust Gwen again) and I think it's unfair people of Camelot to remember him like that because he was the most honorable and noble knight - Lancelot is not my favorite but I cannot deny what's right and what's not.

Lance's dead anyway, so it's not really going to affect him either way. Not to mention how he was meant to be all honorable for topping himself or something like that.
Gwen doesn't have the trust of both herself and Arthur, and that's just not fair.

For Lancelot, because everyone thinks about him like a traitor, and he wasn't :(

For Gwen so she can stop feeling guilty.
For Lancelot to clear his name and to be remembered with honour and dignity
AND for Arthur to allow him to trust Gwen (and restore his faith in Lancelot) again.

Actually I don't care.

because he should be known as the honorable and noble knight that he was, and not as a traitor