My favourites (and reasons) are listed below (some mentioned by others), but the big items for me are something quirky or unique about the airport, and having immersive ground textures.
Wellington (NZ) by Flightbeam - the textures are excellent with ‘wet’ patches, they have captured the gentle slope on the runway perfectly, there is a quirky section to the terminal, and its position means approaches over water from either ends. It is typically very windy there so has the added challenge of strong cross winds
Nelson (NZ) by NZA - great textures again and nice approaches with water masking. Nice Terminal building as well, and great for ATR flights to Wellington - probably not 737 / A320 territory.
Manchester and Birmingham (UK) by Macco Sim - these are larger airports, but the textures have a nice feel to them and they have sloped runways, with Birmingham being like a rollercoaster which make each landing slightly different and more to think about.
Leeds Bradford (UK) by Orbx - this is the king of sloped runways and the runway textures are spot on. The touchdown point is right when the runway starts to slope down hill. Inibuilds also have a version of this and it looks similar to the Orbx, with maybe a few more enhancements in the terminal.
Hamilton Island (Australia) by Auscene - great part of the world, great texturing and excellent modelling of the terminal and essentially the rest of the island. Great water masking on approach. Also a short hop from Mackay (Orbx) that has a nice realistic feel to it as well.
In this same area of the world are Rockhampton and Gladstone airports (Orbx) that have great texturing and places I fly to often.
Anything by FlyTampa usually gets the nod, purely for immersive textures.
I do like Bristol (UK) because of its sloped runway, and I also like Liege (Belgium) by M’M Simulations for similar reasons - although this is more a gully at one end of the runway.
Porto (Portugal) by MK Studios - sloped runway and nice ground textures and an authentic feel.
As mentioned before, more GA than commercial, but the NZA regions of Milford Sound and Mt Cook are great and I am looking forward to their upcoming Wanaka.
I also visit Alice Springs (Australia) by Impulse Simulations a bit and the ground textures there are spot on (visited IRL there back in July). It is a long way from anywhere unless you are doing charters to Uluru (Ayres Rock airport Auscene) or RFDS flights, but was a storage area for planes during covid. No sloped runways there, but an authentic feel.
There are some freeware options that are worth checking out including
Bergen (Norway) - again, a dip in the runway:)
Vigra (Norway) - nice approach and texturing including grooved runway
Jackson Hole (USA) by Old Dogs(?) has some great textures as well as being a nice place to fly into.
With a bit of thought I could probably double this list, but that will give you something to check out.
sorry, subjective word… maybe warmth is better) I’m looking for but its definately one I keep flying into.
