I’ve said it before, and I’ll say it again: ST:TNG.
I’d serve on a cool starship, exploring strange new worlds, but still be able to kick back on the Holodeck, visiting Middle-earth and 221B Baker Street now and then (and even the Firefly 'verse, come to think of it, if we assume that it’s fictional to them).
I think I’d enjoy living on Urth, preferably in Nessus. Something about that dying world appeals to me.
What’s this Fifth Imperium? I can’t find it here: http://en.wikipedia.org/wiki/List_of_fictional_governments
Chalk me up as another one for Middle Earth, specifically Rivendell.
Hmm, just realised I didn’t answer the question myself. Much as I am a SW fanboy, I really wouldn’t want to be an average human living there. Superweapons get into the wrong hands far too often. I think i’d go with Futurama and duel Marley23 for Amy.
DC’s Earth-Two. I already have the wardrobe.
I wanna live where everybody is "clear’-no more evil body thetans lurking around! With everybody clear, there’s no need for work-you can just creat what you want.
How do I get clear?
That’s the first place that I thought of - Cicely, Alaska.
And with everyone else off living in Middle Earth and various Star Trek worlds, it won’t be too crowded. 
Try Windex! 
The insane world of John Water’s Baltimore!
This – http://en.wikipedia.org/wiki/Scientology#Auditing – explains more or less how it works. But not what it costs.
I was going to say the Farscape-verse (Dibs on Chiana!), but on second thought, the Futurama-verse would be good too, i challenge you all to Claw-Plach for Amy!
I would take a one day vacation in Noel Streatfeild’s shoe book universe, 'because it would be the cheesiest pick but still interesting.
From Sixteen Candles to Home Alone, I’d be the coolest, baddest black dude in John Hughes’ movie universe of Shermer, Illinois.
I’d be the only black dude in Shermer, Illinois.
I change my mind!
I would want to be in Tove Jansson’s moomin land. For a few days or so. A lifetime would be a bit too challenging on the psyche.
I thought there were some black dudes at the Mall? Maybe they had to drive in though to work.
Jim
Oooo…possibly Marvel, and I’d hire supervillians to create my own Fearsome Five! Or possibly just chase Black Cat around with a helicopter.
Possibly the Highlander universe. I’d really have to get started in the gym, though.
Or…the Ultraviolet world. It’s English, full of hot women and vampires! Fun!
I had no idea. Bree sounds good!
I would not mind being a resident of the Bazaar on Deva from Robert Asprin’s MYTH series.
10-15 years ago, when I was in shape, Thieve’s World Sanctuary would have been nice. Bet I never would have gained all those pounds if I lived there.
But my all time favorite fictional universe place would be Pine Cove, CA.