Exploring isn't a good way to make money, so you probably want to think about why you are exploring before you head too far down the path of "what's the best value to scan". Revenue from Exploration is really for
1) getting a better explorer (maybe 25m for a top specced Asp, a lot more for the 'conda).
2) getting explorer ranking.
High value stellar exploration targets have largely been discovered in the "near" region as others have already scanned them, but you can still get good money from rescanning them. Sag A* is worth over 300k on its own if you get that far.
If you are just aiming to maximise return then there are belts of millions neutron stars to scan (search for Dognosh's thread on neutron stars and his holo guide). These are guaranteed sources of good value (unlike planetary bodies) - even when they've already been scanned by someone else. Activity searching the galactic map for those on your route is a good idea.
For planetary bodies you get 500 Cr for every body you pick up with the ADS. If you are only after maximising revenue then I suspect that after that potential ELWs water worlds, ammonia worlds and terraformables are really worth travelling any distance to scan. An ADS scan on another system will be more profitable and give an opportunity to find new high value targets. So jumping to a new system will probably give you a better return. I don't think there is a reliable method of detecting terraformable high metal content and rocky planets though, you can look at scanning only potentials in the goldilocks zone.
I think this is missing the point of exploring personally. Seeing new and unusual stuff, and getting to stick "I was here first" graffiti is what its really about
