Neither of these books is suitable. . . These two books are based on the mathematical analysis you have studied. You'd better find a textbook to teach yourself. I recommend Mei Qiang's mathematical analysis. If you want to know more, you can look at Fichkin's. . . It is a complete book and a pit. As for books like Zhuo Ritchie. . I can't say it. If you really want to choose those two books, Apostol's is better, more detailed and less difficult, but the exercises are difficult.