A-Rod.
Phelps is a 23 year old kid. He's going to experiment to the same degree as any other 23 year old kid out there. Phelps didn't gain anything from smoking pot. A-Rod on the other hand engaged in something that is frowned upon by society as a whole, is NOT generally "experimented" with and reaped benefits from doing so (i.e. enhanced performance, money, fame, etc.).