The only thing better than unification is semi-unification. The fact that semi-unification is a lot harder than unification has meant that imperative OO languages get the shaft with poorer type inference support: both assignment and subtyping are inequalities! What Scala has done with least-upper bounds is absolutely heroic in that context even if it does work better for its functional parts.
I'm not sure if "better" is appropriate in this context; in general, semi-unification is undecidable. Type checking in presence of subtypes is decidable for simple cases (where types form a lattice), but the presence of polymorphism/generics makes it undecidable (Java [1], OCaml[2]). The type inference algorithms for subtyping are not that performant (an algorithm is described in [3]).
