Best - FFVII world map theme, Terra, Searching for Friends, Suikoden World Map theme (first and second games at least).

Worst - BoF III is some troutty elevator music, but I kind of dig it, so not sure. Actually Dragon Quest is pretty bad, but not sure if that should count because of how old it is. Still, if you compare first FF to first DQ, the difference in music is significant. Honestly, the games with the worst world map music probably just have music that isn't very memorable so I won't think of it unless someone else brings it up maybe.