In general you pay for what you get. I do have a Gamo and got one on price and availability at the time. I have spent on it thou with guide kit, trigger tune and a lothar walther barrel. This has turned it into a whole better gun. I am now happy with what I have.
Some of the makes you mentioned I would have gone for if they would have been available to me at the time especially the german ones.
Gamo are a middle of the road gun and that is what you get for your money in that bracket. Spend more and you will see better build quality and probably a longer working life.