I decided to do Percy Jackson next because I'm in the middle of reading the first book for the second time. This is a bit long, and I apologize if I do not have all the major characters from the books. There are really just too many of them.
So here you go:

1. Percy or Annabeth?
My answer: I like them both very much, but I'd have to pick Percy.

2. Percy or Grover?
My answer: Percy.

3. Percy or Tyson?
My answer: Percy. But I really like Tyson so that one is a pretty hard choice to make.

4. Percy or Thalia?
My answer: Percy.

5. Percy or Nico?
My answer: Percy. I really like Percy, but Nico is pretty cool. :)

6. Percy or Luke?
My answer: Percy.

7. Percy or Clarisse?
My answer: Percy.

8. Percy or Bianca?
My answer: Percy. I like Bianca too, though.

9. Annabeth or Grover?
My answer: Annabeth.

10. Annabeth or Tyson?
My answer: Tyson.

11. Annabeth or Thalia?
My answer: Annabeth.

12. Annabeth or Nico?
My answer: Nico.

13. Annabeth or Luke?
My answer: Annabeth.

14. Annabeth or Bianca?
My answer: Annabeth.

15. Annabeth or Clarisse?
My answer: Annabeth.

16. Grover or Tyson?
My answer: Tyson.

17. Grover or Thalia?
My answer: Thalia.

18. Grover or Nico?
My answer: Nico.

19. Grover or Luke?
My answer: Grover.

20. Grover or Bianca?
My answer: Bianca.

21. Grover or Clarisse?
My answer: Grover.

22. Tyson or Thalia?
My answer: Tyson.

23. Tyson or Nico?
My answer: Tyson.

24. Tyson or Luke?
My answer: Tyson.

25. Tyson or Bianca?
My answer: Tyson.

26. Tyson or Clarisse?
My answer: Tyson.

27. Thalia or Nico?
My answer: Nico.

28. Thalia or Luke?
My answer: Thalia.

29. Thalia or Bianca?
My answer: Bianca.

30. Thalia or Clarisse?
My answer: Thalia.

31. Nico or Luke?
My answer: Nico.

32. Nico or Bianca?
My answer: Nico.

33. Nico or Clarisse?
My answer: Nico.

34. Luke or Bianca?
My answer: Bianca.

35. Luke or Clarisse?
My answer: Luke.

36. Bianca or Clarisse? 
My answer: Bianca.