PTAC replacement options

I would like to replace a Suburban Dynaline 3 PTAC, natural gas, 20000/14000 BTU heating/cooling, with something better. My main complaints are that this unit has required replacement/service 12 times over 4 years, and that it doesn’t sufficiently heat or cool the space, which has high ceilings and is about 14″ x 24″. Is the Islandaire version enough of an upgrade to be worth it? Do I have any other options that will fit the space, be more reliable, and provide more powerful heating and cooling?