I always do 3x3 rooms for my commoner dwarfs. Its not the most space efficient but helps in generating happy thoughts for the dwarfs as a rooms worth includes the floor and walls along with furniture. Later on smoothing and engraving the rooms further increases the strength of the happy thoughts. I also tend to use the planning mod DFhack plugin to auto place the materowork/exceptional beds in the rooms and use the lower quality beds for my hospital and dormitory, selling the excess so they don't take up space in stockpiles. As for furniture a bed of course and a coffer and later a cabinet as well.
Cons:
I'm making 3 beds for every one I end up using.
The small increase in tile size per room adds up, making the living areas less space efficient which in turn adds some travel time for dwarfs getting back to work from a nap.
Pro's:
Higher value rooms counter act happiness loss, the more of a buffer you have the more stable your fort will be.
I think it looks better on my screen then cramming dwarfs into as small of rooms as is possible.
When I give that 11 skill presser a room fit for a noble even though hes not worth the booze he drinks I feel like a much nicer person then I am in real life.
https://www.youtube.com/watch?v=TN5Xpeq_LN4 Move to the 35 minute mark for a visual on how I stack them to mitigate some of the cons I mentioned.