What's the difference between EnityPlayer and EntityPlayerMP and Which one should I use?

Hi I am making a Mob which solely hunts players. Now on paper that doesn't seem so hard and in fact, is incredibly easy! Until I noticed that there are 2 instances of Players. EntityPlayer and EntityPlayerMP. Now I know EntityPlayerMP stands for Multiplayer but the thing is, I'm not sure if I pick that it would run on Singleplayer as well! Now All I really need to know if EntityPlayer is the same as EntityPlayerMP and would work in both Multiplayer or Singleplayer or would I need to check if the world is multiplayer and pick the corresponding entity.

Which one should I use?

Thanks in advance, Supes.