I myself found the Sorcerer the best to solo. With the right spells chosen, he shouldn't have too much troubles. I did all the Athkatla's side quests without reloading (ok, except for Kangaxx).

I started Kensai once, but I was not sure when should I dual it to mage.

I never tried that Ranger/Cleric though. I'll give it a shot seeing as how you all speak of it.

Try the Totemic Druid. One of the most underrated classes out there. Mid/Early game: Fire Elementals/spirit animals. Late game: Fire Storm/Devas/Elemental Princes.