Pros and cons with each, #1 is probably the first I'd dismiss for many of the reasons you mention. All have issues with an uneven floor, #3 would probably sit tight, but torque out a bit and make the top a bit uneven (twisted).
With legs, if the load is low enough, you could add threaded inserts into the floor ends and use threaded feet. Would only take a minute to screw at most two feet in/out to get level and firm.