The new stock 2k3 Cocker with hinge frame is not a bad choice, had a play with one Sunday and the hinge trigger compared to the plastice one which came with 2k2 version is a great improvement and the milling isnt to bad.
I know it doesnt come with nice shinney pnematics at the front (standard brass) but they are as good.
The cocker will happly run on Co2 but with the little money you save over the imp you could invest in an air system, better barrels, etc.. and in the future if needs be you can eblade it up which seems to be what everyone is doing.
but the proof will be in the pudding - go to planet hold them, see if they will air it up and let you take a few pulls on the trigger because some people don't like the pull of a cocker trigger and prefere the mouse click of an electro and vis-versa, personally I don't mind and have electro (angel) and a cocker.