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Personally, I only use two wheeled bags, half the failure points of wheels, and move much easier on uneven or soft surfaces - four wheels can be similar to roller skating on a beach.
Right now I use a roller hockey duffel for my gear. It's huge -- larger than the max size allowed for checked, free bags -- but it holds everything easily. It's getting pretty worn out though. I will probably buy another similar bag but was wondering what else is popular. I don't want anything with a dive brand or logo on it, as I don't want to attract attention from baggage handlers. It does not need to be carry-on obviously, but it could be slightly smaller than the hockey bag. It must have wheels and ideally the wheels would be replaceable rollerblade-style wheels.
I've only had wheel failure on the one bag and it was the two wheeled duffle with the extending pull handle. None of my other bags over the years have suffered wheel failure. I love using a couple of fingers to guide the four wheeled bag through the the airport.