I have to repaint several interior rooms, and the spray vs. roll question is now at hand.  One rooms has electronics gear in it that I can move or cover, the rest are just furniture.  There are no doors between most of my downstairs rooms I'm painting (dining, hallway, living room) and the kitchen, so that might be an issue.  

I have a respirator, time, and the option of getting either wagner power roller or sprayer to use for a short time.  And 11 gallons of paint.  Each room is going to be one color.  

Any reason to get one over the other?

Prep is alot more intensive for spraying and once your commited, you have to finish.
With a roller and brush you can just prep each area as you go. Doing the cut-in's is the only real time issue and once you "get the hang" of it, even that can go fast. Do remove the cover plates, but don't worry about masking area's for the cut's, just get a good angle brush, a clean wet rag and a small drop cloth and go to it.
Rolling the fields will go real fast.

overspray is a PIA.
spraying is no faster unless you are clearing out the house.

Roll.

Definitely roll.

The reasons have already been laid out in this thread.

If the Power Roller works like it's supposed to, the job should go just as quickly as the sprayer.

I'll be replacing the wall plates after I paint, so they'll all be gone anyways.  Looks like rolling is the big winner.  woohoo!  Go Roll go!