Near said L was the best but they can surpass L if Near and Mello worked together. So in my opinion i liked both of them. (I'm starting to hate Light) If i were to pick one, it would be Near tho. :P
I liked L the best. He was lights perfect character foil even though Light surpassed him. Near was not experienced enough. But I did find it amusing that he played with the lego men while trying to solve the case. Mello was ruled too much be emotions. If I had to chose one, I'd chose Near. He was truly a better detective than mello.