Your trace geometry and layer stack will have a major effect on signal integrity as you route high frequency analog signals throughout your board. Newer designers will likely default to a microstrip geometry, possibly with guard vias to provide isolation between different circuit blocks and to suppress radiated emissions.
The question of which trace geometry to use is about more than isolation; it is also about avoiding losses due to dielectric absorption, roughness losses, and scattering from your PCB substrate.
The alternative to using microstrip transmission lines is to use stripline transmission lines.
Routing striplines on a dedicated interior layer provides isolation from the surface layer, although cavity resonances and radiated EMI from substrate edges can still be a problem.
A better transmission line geometry is grounded coplanar waveguide (GCPW) routing. This is much better for routing on a surface layer than microstrip traces or stripline traces. This geometry provides much lower losses and stronger isolation compared to these other two routing schemes.