Furnace Filters: Flat vs. Pleated - which is better?

Raindog, I’m probably using the wrong terms, but I’ve heard that you’re supposed to get both the outside compressor and the inside compressor (or is it the condensor?) cleaned periodically. Problem is that the inside ::whatever:: is usually located inside a duct and that accessing it requires cutting the duct to clean the unit. Because it’s never cleaned, I’ve heard, it leads to premature failure of the compressor.

I’m not sure what I’m talking about, as is obvious, but can you address? I’m talking about a straight AC system, not a heat pump.