Usually LLanding is the best option, but can be countered by well timed impromptu attacks who can outprioritize Luma's (read:almost everything non trascendental).
Usually AD is the worst option as long as the enemy attack has enough hitlag or hits that Luma just prolongs them to the point of extending to the endlag.
Perfect LLs can be very hard to counter, especially if the LL'd move is Bair because of his superior range and priority, it also has the second largest window for early autocancel(4 frames), second only to Fair(5 frames).
You may want to desynch Luma just for the sake of not having an ultra-nerfed AD, but since he always tries to be at a set distance from you it'll hardly do anything else until you actually land, as nobody has a hurtbox large 1/4 FD, furthermore, you can use it safely only starting from a certain height.
Just like what a disadvantaged state is supposed to be like, you need to overcome your opponent's mindgames with yours, and of course it largely depends on who wou are facing, though against nobody throw an aerial at point blank unless it's a perfect LL. Spaced Bair can be fine and so does the back hit of Nair if Luma is with you, don't even try to Dai ror Fair
