Well, here's a question: what kind of genres/style do you like? One of the coolest things about having so much activity in the forum is that there's lots of different types of campaigns and stories.
My favorites are jonrog's Dark*Matter, barsoomcore's stories (either one) and drnuncheon's Freeport stuff. Wicht has some really good Kalamar story hours too, and the old Byzantine on the Shannon is one of my favorites as well. And both Rel and Old One have a shared world with some cool stories too.
Sepulchrave's story hour is absolutely fantastic. It's high-level adventuring with deep, interesting politics and epic combats. Plus Sep's writing is the best I've seen on these boards, rivaling Robin Hobb and putting pretenders like Terry Brooks and David Eddings to shame.
I'm also partial to Piratecat's Story Hour, but I'm a bit biased there.
I'm partial to Blackdirge's Metamorphosis story hour... I'd read everything up to the end of January, but I've been unable to sit down and catch back up again though...
Sepulchrave's work of art, Piratecat's storyhour, and Jonrog's deeply disturbed Dark*Matter game are my current favourite Story Hours. Going back a bit, RangerWickett's Savannah Knights is another great favourite of mine.
What I've read of Sepulcrave's I liked - but I haven't had time to go back to the beginning, esp. since I would like to catch up with Old One's (another of my favorites) first.
As for PirateCat's question:
I like ones like Old One's - a little grittier and deadlier and that explores a unique world.
I like Sagiro's because it gives me the same feeling as an adult as reading Avenger's comics as a kid.