An i-Pod is the brand name of Apple's (range) of MP3 players.
'Best' depends on what you want. When I was looking to buy dh's mp3 player, I was advised that for music fans a Creative Zen was better. For style/cool, i-Pod better.
You will also find though that most hardware/software and general stuff is designed for i-Pod players, and i-Tunes is encrypted so that only i-Pod players will work with it. (Think that's still true, although it may have changed now).