Not really a fan of the themes introduced in R/S/E...
Really liked Goldenrod city in gen II
Azelea's remake (for the Sevii isles), Mauville city, Mt. Chimney, Hoenn's E4 battle theme and the magma/aqua bases are my favorites from gen III
I only like Cynthia's battle theme from gen IV.
Finally, Driftveil city, Elesa's gym and B/W2 Rival and team Plasma themes are the ones I like most from gen V.