Hardest swali ever!! I loved both series! The plot and its twists, the characters and their development- Rick did an amazing job and managed to immediately make me a shabiki of his (to the point where I read the Kane Chronicles as well X3 I can't wait to get my hands on The Crown of Ptolemy!)
Although, if I had to choose, I'd say I like the HoO vitabu the best. It's where the most feels are, plus the characters are amazing. I really enjoyed the romance/love triangles, the battles, the plot twists,, the character development and, of course, Leo Valdez! XD
They are both the same series technically. But Leo wasn't in the original, and he is my inayopendelewa character. But Percy was so much zaidi interesting in the original!