Here is a list of all the best alex rider novels.
1- Ark Angel: Since 1979's Moonraker, sending spies up in space was almost a taboo. But in the sixth edition of the AR series, Horowitz has made it sensational to read and even more fantastic to imagine. Major thumbs up, the best!
2- Point Blanc (or Blank, depending where it was released): An ingenious plot. Usually cloning would be a rather overlooked thing, but it was pitched perfectly in this book. Especially the fight at the end, absolute gold!
3- Scorpia Rising: The last book in the series is one of the best. One of the saddest plots of the series though, with one of the main characters dying. But that makes the book even better. Alex is the edgiest he's even been in the final installment. A classic.
4- Scorpia: A very good book, although slightly overrated. Scorpia is still a good read, with scintillating twists and turns.
5- Stormbreaker: Pretty dry at first, but livens up later on. Shortest book in the series, but still a fan favourite.
6- Eagle Strike: One of the more overlooked books in the series. Entertaining, but not as good as the first three.
7- Skeleton Key and Snakehead: Those two are tied for seventh. Skeleton Key is an entertaining read, but somehow the plot just becomes rather unrealistic and Snakehead was good fun, but it lacked a glue that previous stories had.
9- Crocodile Tears: Probably the most disappointing entry into the Alex Rider series. Although it has its good moments, such as Alex winning the poker game and the car veering off a cliff, the book seems rather strange and the plot sometimes seems a bit ridiculous. I won't give it a miss, but probably not up to the standards of the previous books.