Opinions on Carcass structure

I’ve been watching a few videos on kitchen carcasses/cabinetry and wanted to get some advice and opinions on what others find is the best solution. What’s the easiest to construct, what’s the easiest to level, what’s performs the best structurally? All a matter of opinion and keen to hear everyone’s thoughts. I’ve come across the following:

• 2x4 plinth and the carcasses sit on top.

• Side panels of the carcass directly on the floor with a recessed toe kick

• Adjustable plastic feet

• 2x4 levelled and fixed to wall, Carcass sits on top, and adjustable feet to the front