Best method to prepare catfish (very soft flesh)?
Dredging in lightly salted cornmeal and then frying (shallow frying is fine, but deep frying is magical) is an absolute classic in the Southern US, where catfish eating is big. I usually just put the plain filets in the cornmeal without first dipping in egg or milk. I don't think it's necessary--though I'd go with milk if I were forced to use something. After dredging, I let them sit on a wire rack for a minute or so before frying to set the cornmeal (which I would do if using egg or milk also).

Generally, though, most treatments that work for a mild, tender white fish will work. Recipes for flounder or sole (Sole a la Meuniere for example), or ones that look for rockfish or striped bass will work really well.

Bear in mind that catfish does have a distinctive flavor, though it's not really strong. Some people don't care for it, and they tend to describe it as "muddy" tasting. Personally, I don't see it. If you like the catfish OK, but find the flavor intrusive in some applications, adding spicyness or acid (lemon juice, vinegar) will mute it.