My order is:
1. Armin van buuren,
2. Above & Beyond,
3. Ferry Corsten,
4. Paul van Dyk,
Why I consider Armin the best producer of these listed above? Because he's the only producer whose tracks (some of them) get stuck in my head and keep playing and replaying even 3 or 4 days after I listen to them. I go to the bed, and next day when I wake up, the track or continues to play in my head.
Orbion, Mirage, Desiderium 207, Blue Fear, Communication are just some of them... And what's weird, I just like all the tracks on his albums. All of them.
On the other side, Above & Beyond produced some of the world's best vocal tracks (their OceanLab project), which I really love, but when it comes to choose between Armin and anyone else, I choose Armin.