While I've found valuable planets in most system types, Earth-like planets are most likely going to show up in similar systems to Sol. Sol is a type G star, so those are good to check out. Type K is one step cooler than G, so they are pretty good as well. Type F is one step hotter than G, so those are useful to check. High metal content worlds are more common and show up in most system types, though hotter is usually better, to a point.
I guess that my point is that you can find good planets anywhere, but F, G and K type stars are a pretty good bet.