As a 3rd generation fanboy, I'll add my numbers to this =D
Sapphire- Once. I had Ruby growing up and my brother had Sapphire, so I never really had a chance to play this, but we decided to trade the games once and do a playthrough of each others versions.
Ruby- Around 10 times. I loved my Ruby version and I really wish I still had it. This was my first gen 3 game and I will never forget it.
Emerald- This is my favorite game of all time and I have played it at leas 30 times. This is a game that I can never grow tired of!
Firered and Leafgreen- Listing these together because I have played them around 10 times each. I loved these games and I don't think I could grow tired of them either =D