My older sister. My other sister doesn't really like the same things as me (not that I dislike her, it's just not as fun to be around her because we have different interests), and my mom is nice most of the time but she can be pretty annoying too. I haven't seen my dad in several years, so I'm not really counting him.
I don't know if I have a 'favourite'- my parents, as much as I do love them deep down, annoy me to no ends if I spend to long around them, as does my sister... As for more extended family, I have what, 17 cousins? I think, and at least 7 children by those cousins, so it's kinda getting hard to keep track of them all. Mind you, what am I complaining about, my dad had over 50 cousins...
I do tend to get along well with most of my relatives though. My dad has four brothers and they all seem pretty cool and funny. My mum's side is a little more iffy... Though they're still nice people I guess.
Well, that was tl;dr now wasn't it. I like my right hand, does that count as a relative? There you go.