5 Volt Regulator 120 mA no Heat Sink
A switcher will almost certainly be better.  You should be able to find a buck module that will drop 18V down to 5V.  Shop carefully -- there's older design modules out there that aren't very efficient.  You should expect 80% to 95% efficiency.
If you're willing to go for it, you can build a switcher onto your board from one of the many chips out there.  If you're constrained to a through-hole design, though, I recommend that you just get a module.