a properly sized and leveled poured concrete pad...

The pre-fab pads work fine if they are placed on a leveled base of pea gravel.

I like the concrete and foam form ones better.
The foam is all on the bottom and not exposed.

UV from sunlight is very hard on almost all plastics unless they are loaded with solids (chalk or carbon black are common) to provide an absorption layer.

The very surface still is damaged, but the UV cannot penetrate further into the material.

the plastics dry out from uv and crack
the skim coated foam ones are ok until the
skim coat is damaged then the foam degrades.

granted a concrete pad poured in place is better
but if not offered by your hvac company it may be
something you need to delay your install for
and diy or hire out. if these are the two options
they offer you they prolly won't pour a slab for the
condenser.

best of luck.

Raising the unit 4" above the ground helps keep the fins cleaner and helps prevent blocking from moderate snows for heat pumps.