Flash-memory based players
Flash-memory players take USB memory sticks, SD cards and/or CF cards and output video signals over a VGA, component video, or HDMI connection in high-definition and possibly as a composite or S-Video connection in low-definition.
In general you want to pick a player that provides a high-definition output matching your choice in display. The one case where you might want to use a standard-definition output is if you are modulating your display onto a TV channel for distributing into rooms in a hotel or other location with standard definition TV screens.
Flash-memory players tyically support all common forms of flash memory including USB Sticks, SD, CF and MS cards, so that’s rarely a point of differentiation: you can simply select whichever card type you prefer depending on what slots you have on your PC or laptop. USB sticks tend to be the cheapest form of media but they tend to stick out more than an SD or CF card would which may not be desirable.
If your player is going to be mounted in a public space you might want to consider a lock-box enclosure for it, and/or the memory card so you can prevent it from being removed or turned off.
Flash-memory players may support standard definition video, 720p high-definition video or a full 1080i or 1080p high-definition video output. If you decide to go with a VGA connection between your flash memory player and your display make sure it can adjust to match your display resolution and isn’t instead fixed at a resolution like 1024×768.