TheArtisticOnion

They are just different.

Sovereign was this scary, mysterious figure that had to be taken out by entire fleet.

Harbinger, on the other hand, has two sides:

I admit, he is funny, he generated a bunch of memes and won't shut up during a fight, but... I think that that's what kept my morale up when I was playing the game, otherwise I'd probably kill myself when he was ASSUMING DIRECT CONTROL of another Collector I was about to finish off. ME3 Harbinger is mute and absent, so he doesn't count.

But many people forget, that he actually tried to make sure that his enemy is dead. Maybe because he is the oldest Reaper, he saw most of the battles in the galaxy and he's careful about what he does. This also leads to another thing: If he's the oldest Reaper and there is only one to zero Reapers created per a cycle, then there had to be a moment when he SOLO'D THE ENTIRE GALAXY, because there weren't any other Reapers around/they were yet to be created.

In my opinion, Sovereign is this scary af, but not careful type of villain who can give scary speeches and be scary in general, and Harbinger is this, at first dumb and funny type of villain who needs slightly more attention to prove himself as a good character.

In other words, they're too different to compare, I like them both, but in other ways, and sorry, but I sympathize with Harbinger more than with Sovereign.