Against Tower, Dungeon is a good choice: Darklings hate Titans and move faster, and Heroes with Tactics allow you to get close to the archers. On an XL map against Solmyr, choose Gunnar with his Logistics skill. Artifacts with a ban on magic are not uncommon on random maps, so don't miss the opportunity to force a battle on cursed lands.
If you enjoy powerful magic, the only one who can compete with Solmyr is Dymir (Starfall). Increase his Magic Power, and Knowledge can be improved with Mana Vortex.