I would say that Garrus is one of the best Bioware LIs to date. Unlike others he doesn't dump you when he becomes king, leave you for years after sleeping with you once, resort to terrorism, accuse you of terrorism, father a child while you're in prison, talk about his dead wife, talk about his dead girlfriend, talk about his dead husband, talk about his dead wife who he himself killed, die, attempt to stab you in an alley or commit suicide. Winner!
He's relatively mentally stable, very emotionally supportive and funny. And he's got a really big... rifle.
Answer key: Alistair, Fenris, Anders, Kaidan, Jacob, Thane, Zevran, Steve, Valen Shadowbreath, Thane again, Zevran again, Alistair again.