I pop in and scan everything, set up to scoop, surface scan the star, then look at the system map and see if there's anything that looks interesting. I don't bother surface scanning balls of ice or rock belts, but if I see something that might harbor life, or may look earthlike or a water world I pop over and scan it. Sometimes I get a system that looks really interesting overall in which case I surface scan everything for posterity.
If I'm heading home I usually make max-length jumps and just bungie in, discovery scan, surface scan the star, and bungie out.
Last night I found a system with 4 brown dwarves with elaborate rings, orbiting eachother. I scanned all of those, because, um, I dunno!
Rockys and Icys get as much of my love as gas giants, earthlikes and the other big boys in a system.
That's interesting!
I've noticed some people like to scan for minerals, some for nice real estate, etc. I scan for life. I love finding signs of life. Dunno why.