Morata will score more in CL. I would bet on that.
What if Chlesea somehow fail to qualify?!
In any case I see Morata and Lukaku as two very different kind of players..
Morata is more about speed and technique, is more of a player that helps the team building attacks while Lukaku is more the give him the ball to finish moves
Finishing and headers wise Lukaku is better than Morata
Lukaku is also a monster in terms of physique while Morata isnt weak himself..
Morata can dribble, hold the ball, is actually quite a fast player and is super clutch
Who is better?! Id say it depends on your team`s needs... I personally would rather have Morata than Lukaku even though in Serie A I see Lukaku as a leading candidate to be the top scorer...