Arduino Networking Schield -- Question

Could I get a recommendation on the network shield I need to get for an Arduino 2560 Mega board. There appear to be many on the market and of varying version. Also, apparently many do not work well with the SD card hardware on the board.

I'm really confused at this point and help would be appreciated. I'd really like to use the shield on my mega to control a robot previously used in FIRST competitions.

Doc