Wow. So much bad advice... For something so simple.
Unused gate INPUTS should be tied , either directly , or thru a resistor , to VCC(supply)
Anything else is less optimal
Tying to ground: if ttl you have a vampire drain because the inputs can source current
Tying to another signal : the gates will follow the signal creating more power consumption (ttl always, more if low, cmos when toggling) and will create more crap in the emi .The more transistors switch the more crap
Input tying to vcc thru a resistor gives the advantage that you have access to the gate if you need to rework part of the circuit.
Now, if all you need is a single gate : get a singlegate logic chip a 74v1g02 should do fine