10/100/1000 ethernet will gives you three speeds to choose from, depending on what network equipment you have. 100 Mbps ethernet is the most common, while 1000 Mbps is gaining ground. *10 Mbps is hardly used anymore as a standard speed.
Most, if not all, motherboards will come with a 10/100/1000 onboard Nic. *100 Mbps speeds are fine for ethernet, gaming, and normal file transfers between computers. * 1000 Mbps speeds are only good for faster file transfers between computers. It won't help with Internet speeds, which are determined by your ISP.