Whose Grifter goes first?
The November 2014 tournament floor rules answers this:


  Before the first turn of the game if there are effects/reacts that
  could be conflicting before a winner has been determined by lowball
  (E.G. Grifter abilities), use the following procedure: 
  
  
  All players make a choice as to whether they are going to use or pass on the grifter ability. Each player then holds their hand out
  with a concealed token in there, with an agreed colour code, red for
  use and blue for no use. 
  If a player fails to hold out a token of either colour then they pass the use of the grifter. 
  Both players open their hands at the same time and use the ability or not as indicated.
  


In friendly games, we usually don't worry about this, and even in tournaments in my experience it is resolved without resorting to this 90% of the time.