Future proofing for 240V outlet
NEMA 6-15 and you're done

Outlets aren't that expensive.  Simply fit the correct one. 



The third one. 

If your wiring is 12 AWG or larger copper and your breaker is 20A, you can fit a NEMA 6-20 instead.  

Now, noting this thing is dual voltage, the right way to deal with that is have it have a removable inlet (the way a PC does) that takes an IEC connector.  Then you simply change the cord to what you're plugging into.  However you can make a NEMA 5-15R to 6-15P cheater cord if you really want to. If someone finds a 6" long cord with a funny plug on it, that's a big fat hint to be careful what they plug in.  

If you are thinking of wiring up a universal future adapter socket, you can't.  What you can do is run 6/3 cable (or #8 THHN in conduit) to a large 4-11/16" square junction box.    The large 4-11/16" square box gives you the room for big wires and splices.  At this point you can install any of these pairs:


NEMA 6-15 receptacle with a 15A or 20A breaker
NEMA 6-20 receptacle with a 20A breaker
NEMA 6-30 or 14-30 with a 30A breaker
NEMA 6-50 or 14-50 with a 50A breaker


Note that except for a 15A receptacle on a 20A breaker, the receptacle size must always match the breaker size.   And of course you can't exceed wire maximums.