If you, like me, like playing on randomly generated maps, I advise you to check out this application. (It's only for TotE, I don't know if there are some older versions available for HoMM5/HoF.)
First, it lets you generate a template with it, then after using HoMM5 to generate a map based on that template, you can also fine-tune the map to make it more interesting (because while the built-in RMG does a solid job, the maps it creates can be rather bland, and there are some design flaws on them, such as an insane number of Obelisks).
P.S. You're advised to read the manual (at least the part dealing with options) before generating a map. You can find that in the first post, too.