I like the logic where a panel is a rectangular box.

I suggest two other alternatives 5 and 6 with a preference for 5.

The logic is that each panel is in a rectangular box so that outside borders are continuous. For the left and right panels, rectangular keys are used since the thick border is sufficiently distinctive. For the letter and punctuation panels, rounded keys are used. In alternative 6, they are always rounded. In alternative 5, the sides abutting borders are not rounded.