Depends on what you're after forbthe most part.
8k 1 has served me nicely with being centralized with the forest biome. However, if I wasn't concerned with stability in the wasteland city, then 8k 2 wouldn't have been a bad option as a wasteland home base would be pretty good.
On multiplayer and another game, I'm using 8k 3 and it's been good for natural progression. Starting in the NE corner, I've relocated counter clockwise to the Snow Biome and have declared the Higashi Pharmaceutical tower as my permanent base. Loving it so damn much.
I tried Navezgane for a short period and absolutely hated it. On Legacy it was a great starting map for new players, yet despite the additional size increase to 6k over 4k, and various new pois and towns, the overall structure is too spaced out to be good. Mostly because Navezgane towns are an absolute joke in comparison to random gen/pregen maps.
Haven't tried the 4th map in each size as the linear design doesn't interest me any. If anything, makes me recoil quicker lol.
And 4k maps, I won't even bother. Far too small after having experienced 8k (and one game on the 6k1 which was also a good option).