SPOILER ALERT: (these are all my opinions, and others may differ.
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The funniest, I think, hands down goes to the Five Flagons Inn (Bardic stronghold). Worth while putting up with a Bard to go through it...it's also a CASH COW.
Most difficult I would think would be the Paladin Stronghold because of Firkraag...but most rewarding if you're a paladin because of Carsomyr.
Most direct management would be the Thieves' Stronghold (you can micromanage five different thieves: a cutpurse, an assassin, a smuggler, a blackmailer, and a catburglar) and get different rewards.
Most unusual would probably be the wizards' Planar Sphere. I don't know how rewarding that would be unless you want a place that will make unlimited potions.
The biggest stronghold is the fighter's stronghold, De'Arnise. It's fairly easy to get early on (even with all the trolls, if you play it right) and it's pretty cool being the master of an entire castle. It's hard to get to in a pinch, though.
The Ranger stronghold in Umar Hills can yield some nice goodies and quests, but all it really amounts to is a cabin in the woods. Not my cup of tea, but others may feel differently about it.
I've never played Cleric so I have no idea what the Cleric strongholds are like, other than you get a room in a temple (and the initial SH quest is pretty tough; the Unseeing Eye Cult.)
Also never have challenged for the Druid stronghold (the Druid grove near Trademeet).
Hope this helps, at least somewhat.
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