I have to disagree on this one.
While ap mode can be considered "easiest" in terms that you can pick whatever hero, many sd or even rd mods can be imbalanced just in "picking phase", just as some heroes are imbalanced if not properly countered, and in sd you don't have the "privelege" of countering them so easily.
At least in public games, where you tend to get random pubbers in team.
I do approve however usage of different mods, and I would love to see them, we had a deer idea about some of "unofficial modes" like -dm but that's not the topic so I wouldn't go offtopic much with explanations.