Are you sure it's the Agility (not Agility 3 or whatever)?
Either way I think everyone will say M4 if not for speed but reliability.
I have an Agility and an Agility 3 and have no problems with either.(Agility 3 is almost twice as fast as the Agility, not that you can really tell in my usage)
However, will probably buy an M4 soon or the OCZ Vertex 4 as it has a new controller.
Its the Agility 3 60GB