Get the King Arms M4, it's a great deal.
Don't forget that to play at Splatters, and really at most games, you will need to downgrade the spring in your gun -- that goes for pretty much all the guns in your list. Get the shop you buy at to do it for you and insist that they ensure that it is feeding and firing correctly in the chrono before you accept it back from them ( a common source of first-time-buyer delays in getting to the "fun time").
Hope that helps
Now you know