Cockers = mechanical/run on c02/high maintenence
Impulse = True Electro/run on co2/little maintenence
Angel = True electro/HPA only/Little mantenence
Whatever suits your style of play, Angels esp the older ones tend to have an arch in their flight.
Cockers being a closed bolts marker are the most accurate, and impies tend to be the favorite for a first tournement marker as there easily set up/accurate, high ROF and there cheap (new or used)
Like toms said: Both of us have had an array of markers and for some reason always end up back with an impy (2K2 Eclipse R.I.P)
I think that says everything