1. Twilight: Edward vs JacobI'm not that into Twilight anymore, but I'd pick Jacob. That best mirrors the choice I made in real life :-)
2. The Vampire Diaries: Stefan vs DamonDamon, of course! He's the bad boy, I know, the very bad boy, but when you start to see the caring side of him... And just look at him!
3. The Mortal Instruments: Jace vs SimonTeam Jace all the way! If you haven't read these books, go read! Now!
4. The Infernal Devices: Will vs JemI have yet to get my hands on Clockwork Angel so I haven't picked my team yet...
(Two weeks after ordering this my online provider of books informed me that their supplier does not have stock. How dare they not have stock? Unacceptable!!)
5. Paranormalcy: Lend vs Reth
Seriously. Who would pick a psychotic faerie? I'm with Lend!
One reason for all the love triangles in YA fiction is that the main characters are young and still figuring out what kind of people they are. Hence, they're also still figuring out what type of guy/girl they should be with. So their journeys of self-discovery are often mirrored by their journeys with the different love interests, until they reach a point where they know themselves well enough to know which guy/girl to choose.
And, of course, there's the immediate conflict created by having more than one love interest :-)
Hmm, a thought: Am I correct in saying that there are far more 1 girl + 2 guys triangles than there are 1 guy + 2 girls triangles?
Wanna tell me which teams you're on?!