Individual puck lights, either fluorescent or halogen is what my clients usually use. The fluorescents last longer and give off less heat, and that's why they are more often selected over the halogen. The summer in the South is hot enough without adding in a zillion watts of halogen heating to the AC load. The halogens do provide a whiter light, but they are HOT! You also have to be VERY careful and wear gloves when changing out halogen bulbs, because if you get any oils from your hands on the bulbs, they burn out in no time. That's another plus in the fluorescent column, as the bulbs last so much longer and aren't as fussy about being changed out.

BTW, if you have the room to reduce the size of the cabinets below, or the room on top, I'd choose 18" stacked cabinets above 12" ones any day. A 12" cabinet really limits your display area to very small items.