Flat and Firm
Those are my requirements. There are many saddles that accomplish that. Flat refers to the portion on which I perch, across the saddle. Flat, not arched. Also, I adjust saddle pitch angle so that the seat portion is level, irrespective of where the nose is (usually pitched up to accomplish this).
Firm. This means that if there is padding, then it must be quite firm and minimal. That's why I like the Brooks Team Pro, Brooks B17N, the Gyes GS-17A cut-away laced, or any of the modern flat saddles like the Fizik Pave CX or anything with that profile. There are literally dozens that are fine.
Firm and Flat. Also, although I do wear cycling specific shorts most of the time, I don't need to for comfort. It's mostly for sweat management and reducing friction on the saddles. No need to wear holes in shorts that aren't meant for cycling.