The key to finding water worlds or earth likes is star class.
They are found mostly around A, F, G, K and strangely often around Neutrons and Black Holes
The gaps between the arms of the galaxy have low star frequency. Less stars means less planets, and stars in gaps tend to be cooler (Red and Brown Dwarfs). They have mostly ice worlds.
The brighter regions in the center and along the arms are denser, better chance of nice planets. Stars in bright areas are often the kind you need for Earth Likes.
Neutrons and Black Holes are most frequent Around the outer center regions (inner center is mostly F/G/K class). Neutrons/Black Holes also appear a lot 1,000 ly above and below the plane, however stars are only reachable there within a certain distance of the center.
One more note, in my experience a lot of brown dwarf fields are below the plane's 0 vertical co-ordinate. So staying between 1-300 above is ideal unless looking for Neutrons/Black Holes.
Edit: also, if you travel around the core, galaxy map will be incredibly annoying. Stay over 1000ly above/below the core or over 3000ly away if you're on the plane.