These switches are normally open momentary type. This means LEDs connected to it will be on only when the switch is depressed. Let go of the switch, the LEDs go out until you press and hold the switch again. This is a nice type of switch for interactive interpretive displays.
The small momentary is nice for small projects. With dimensions of only 4.4 x 4.4mm square and 5mm to the top of the switch, you can hide this switch in even the smallest spaces.
The large momentary switch is a nice size for larger displays. It is sturdy, with a solid stop feel when depressed. The large momentary is also threaded so it can be mounted in a panel. You will want to drill a 1/2 inch hole. The red color is high visibility and both noticeably and inviting to press.