I mean by quality: bug-free, heavy and water-proof.
Water-proof??? The Fluke ScopeMeters would be the only ones that I might consider putting near water. You can always strap a brick to them to make them heavier.
Reliability, accuracy, quality and heavy duty are my primary concerns.
Accuracy is not generally a concern for scopes. Measurements are often based on displayed waveform (<800x600px) information. The time base and trigger counter accuracy might be able to get close to a dedicated frequency counter with the cheapest possible reference clock (~10-50 ppm). Amplitude accuracy might be 1-3% on a good day. For DC. And might be 30% down at its rated frequency. I suggest you do some more research in what an oscilloscope is before you spend your money.
Heavy-duty: if trained monkeys should be able to operate the scope, then I would again refer to the Fluke ScopeMeters. Performance/$, specs, features and UI will definitely be inferior to bench scopes, though.