For 18K BTU I would suggest a split unit.
I have used a brand called TGM that seems to cope quite well. OK, so they are made in china, but what isn't these days?! They are distributed through stores called Refripartes. They also stock all spare parts should need anything in the future.
One feature I like about the TGM brand is that they put the external compressor and condenser in a plastic case. My last AC unit was LG. It only lasted five years until the case corroded right through.
Price wise, I paid about 25K pesos for an 18KBTU split. But that was a couple of years ago.