In my opinion, Dugald is the best choice for small maps. It makes sense to focus on a numerous and strong army, and considering their alt-upgrade, they are quite powerful. Plus, the starting army helps in fighting neutral creatures. Axel is also not bad, but he is useless until the Knight dwellings are built. As for Iris, I like her because she gives un-upgraded griffons the "Strike from Heaven" ability. This allows you to deploy only griffons and eliminate, for example, dangerous archers without any losses. Usually, there are not enough resources to upgrade their dwellings, or it feels wasteful (when playing on veteran difficulty).