I know the Germans are so much better as I have shot a RWS Diana and it feels much closer to a real gun than the cheap Crosmans but IMHO the Crosman's are really nice for the money. They have decent power for pest control and despite having now fired many hundreds, in one case several thousand pellets I have not had any problems.
I would suggest a piston over a spring only because it's lower maintenance, quieter and more reliable. If you're going to sit there looking to snipe off creatures then you can leave it cocked and loaded for a while without deforming the spring.
In my experience in both cases it's not worth trying to seriously use these guns or even sight them in too thoroughly for the first few hundred rounds. Just shoot at things and enjoy for say your first tin of pellets, then clean it with solvents and lube with oil and devices that won't compromise the rubber (I use slip 2000 as that is what I use on my other arms of fire). Then shoot a few dozen pellets more to foul it up, then sight it in. During this time you will have time to practice firing the thing because it's imperative you hold it a certain way with your support hand flat and stretched out, something known as the artillery hold. If you don't do this the bidirectional recoil will spoil your aim. Knowing this very paragraph of info will greatly improve your expectations, accuracy and overall ownership experience, IMHO and with lots of YMMV as well.
