Well, it is really purely subjective.
But
@Demonspeed raised a good point, that Melizabeth's is getting more development and depth right now in the story and we'll eventually see more of their history, like how they fell in love with each other in the first place, which makes the pairing more interesting.
Before this they were just Meliodas molesting Elizabeth whenever the hell he felt like it, him saving her over and over, and her being head over heels for him, which I can agree is not an ideal romantic couple.
But I guess people enjoyed that because they
are the main focus of this manga, and people either love Meliodas or Elizabeth.