If you were to do a quick straw poll and ask everyone what their favourite Mass Effect character was, it's not hard to guess what the top result would be: Garrus. Everyone loves him, most people want to bang him, and he's definitely an asset in any squad.
So to spin things around a bit, let's ask the reverse: what's the worst character in the whole series?
I've already stated my dislike for Miranda, although that's partially down to her personality. As a squad member she's incredibly versatile, although I found Samara was more handy as an all-out biotic specialist and Grunt/Garrus more useful as raw fighters. She does have the complexity of the relationship of her father to go off as well, a depth not all the Mass Effect roster can boast.
But for truly awful characters? There's Morinth, a true psychopath who takes her mother's place in your squad and can even kill Shepherd, if you want to walk down that path. But perhaps the worst crimes are committed by Jacob and Kaidan, both of whom are just boring.
Be a masochist. Set the world on fire. Or be the best friend Shepherd or Ryder has ever had. I don't mind. But whatever you do, don't be dull. That's what makes for the truly worst characters, and it's why Kaidan is my pick for actual worst. (Jacob's equally bad, but at least there's a laugh to be had in how shitty his romantic lines are.)
What's your pick for the worst Mass Effect character in the series?