The Son of Neptune because we got to hear Percy's POV again! (even though it was in 3rd person) I honestly thought the second book was a lot funnier than the first, and it kept me wanting to read (unlike the Lost Hero-- it was good but i thought the Son of Neptune was better).
In my opinion I really liked both books. I liked The Lost Hero because it introduced new characters to the Percy Jackson series. I also liked The Lost Hero because it had the original characters within the book to help you understand the plot if you didn't read the Percy Jackson and the Olympians serious. I liked The Son of Neptune because Percy was back! It also introduced new characters and was all around amazing. It kept me reading till the end.
I luv both of the books but... I'll have 2 go with the Son of Neptune, because everything is more epic when Percy's involved. Plus the cliffhanger was way better in the Son of Neptune, than in the Lost Hero in my opinion.
Go Son of Neptune!!!!!!!!!!!