Scattered or clustered?

Scattered, because it makes most of the map important. With clusters, there can be huge gaps in the map. Not too much fun to have this huge section of map where there is no action. You know, "Nothing out here in the bottom half of the galaxy except Starbase 134 and 562. Nobody's gonna come all this way where no one lives just to blow up a couple of resource refineries."

Tight clusters. Range matters, starbase placement matters, and culture gets concentrated more along with pop.

I prefer clusters.
It leads, in my opinion, to interesting situations which are not possible in a scatterd game.
For example, on my actual game (large), there is one cluster on the bottom with NO major civ in it at the beginning. Between that cluster and the rest are about 6 sectors of empty space. So the first civ able to send a colonyship over that distance will get the planets down the: A much longer colonization phase, everyone trying to bridge that gap with space stations and range+.

It's a matter of taste, but I prefer that kind of challenge to a map where every sector is of equal importance.

I find that I prefer a fully scattered map. It feels more realistic, as the stars in the galaxy are evenly divided as opposed to being lumped info a few groupings.

Besides, it reduces the probability of a poor start on the larger maps.

Loose clusters here. I like that on larger maps it produces galactic geography as opposed to just a homogenous ho hum spread.