Necro is one of the easiest (archer and lightning mage are also pretty easy). But I never use the summon skeleton skill -- life drain is brokenly powerful.
Depends on what you mean by stinks. Strength? Fire mage is a reasonably easy win. Enchanter is pretty powerful, too (if you can survive the early levels). Melees are tough unless you get a good weapon.
Necromancer is an easy win but so slow. I can only get speed if I use contagious disease instead of summon skeleton. But that's risky. Lightning mage is OP tho.
It's pretty easy to get talents that provide elemental resistance. Mages also don't start out with any additional damage with their own element, either, from what I can tell. They need to learn both of those along the way.
For level 9 (the circle), I put three units guarding the exit. Focus on getting those guys fairly highly leveled, then start adding toward the entrance.
WryleA. Hard to know without knowing where you're at. All melee is difficult, for instance, and would need different advice. Maybe these are obvious things, but (1) make sure you're fighting at an appropriate level... check your enemies before fighting them, and (2) hire mercenaries.
 "Rogue Fable III"){kind=icon}
 "Poker Quest RPG"){kind=icon}
 "Incursion"){kind=icon}
 "Wondrous Lands"){kind=icon}
 "Three Goblets"){kind=icon}
 "Tank Biathlon"){kind=icon}
 "Midnight Spooks 2"){kind=icon}
 "Aground"){kind=icon}
 "Save To Kill"){kind=icon}
 "Realm of the Mad God"){kind=icon}
 "Awesome run 2"){kind=icon}
 "Shadowless"){kind=icon}
Master Po -> adventurer branch