ANSI layout is the standard layout used in the United States and many other countries. The ANSI full plate will include cutouts in this layout to provide support for the switches.
ISO layout is the standard layout used in many European countries. The ISO plate will include cutouts in this layout to provide support for the switches. If the enter key on your keyboard doesn’t look like an inverted L-shape. you will most likely want to go with ANSI.
ANSI Half is a plate with one large cutout for the alpha cluster. This allows switches in the alpha positions to take advantage of the flex cuts in the PCB. If you select the Half plate option, you must pair it with a soldered PCB. If you select the hotswap PCB, you must select a full plate (either ANSI or ISO).
For plate materials, bottom-out firmness and acoustics are considerations of preference. In our experience, softer materials may help reduce finger fatigue for long typing sessions, while firmer materials may provide a more responsive feel. The order of plate materials from soft to firm is POM, FR4, CF, Aluminum, Copper, and Brass.