Over their iterations, my fortresses have evolved to utilize a common , specific floor plan. Reason for this is the designate tool; this design evolved to be as easy as is practical to create using the current keyboard commands (direction keys, shift + direction keys). I do use the mouse for the fiddly bits, but it's a great timesaver and a really simple layout. I thought I'd post it here for general commenting if you are so inclined.
The basic block is a square 41 tiles (starting tile + 4 * [shift + direction key]) wide; I outline it by designating the area around it to be dug out, with stairs at the corners (I usually dig roads that are 3 tiles wide, but that is mere laziness / preference). The resulting square of rock I divide into nine smaller squares by digging out four intersecting tunnels, like so:
Yes, one stair is placed out of line. Curse my bad aim with the mouse.
That gives me exactly 11 x 11 squares, or exactly the starting tile plus one shift + diagonal direction key, of floor space in nine rooms to designate for digging. I use either the mouse or the keyboard again (there is an easy layout for those too) to designate doorways. If I want stairs inside the rooms I designate them with the mouse.
This 11 tiles of floor space in a room can be all one single room, or further divided into four 5x5-tile or nine 3x3-tile rooms (if you want them all the same size) simply by undesignating with the keyboard commands and then using the mouse to place doorways.
This used to be the basic design for everything, but the residential area has slightly deviated from this basic floor plan. I used to lay out the residential area with the same basic design, making the central 11x11 -tile square a market or a barracks and have the four adjoining squares be hollowed out as living cubicles by having a 3-tile wide road in the center, from the edge of the block to the central square, accessed by small 3-tile rooms (coffer, bed, cabinet) branching off it (this gave me 12 rooms per 11x11 square) This gave too cramped access to some of the hallways, so I flipped the design of the cubicle areas, positioning them in the center and making them access the much widened side hallways instead, also adding two additional cubicles per square like so:
The central room is a dining room / meeting hall with a prepared food stockpile. The lower corner rooms are part of the baroness' and the baron consort's apartments, and the upper corner rooms are being prepared for the royals. Only counting the commoners' rooms there's 56 apartments in this block, so 4 of these blocks would house a fort that has reached its immigration cap -indeed, there are three additional floors like this one, all stacked on top of each other.
Aboveground, I do this:
The 41 tiles long walls are great here too, since walls can be designated in rows of up to 10 tiles wide currently, meaning that ideally (if it weren't for the intruding water that I don't want to wall over right now) I'd get by with 16 total 10-tile wall designations to wall in the entire yard, leaving a quite safe area of the surface for my dwarves to utilize as they like.
So. Pros are the minimal effort needed to designate for excavation, the accessibility (pathing lag only becomes noticeable when I designate a couple hundred rocks for dumping) and the total disregard for any and all natural features you can display by extending this design to the surface or through a chasm.
Cons are that it's, well, unimaginative. It also takes some extra digging compared to a typical branching fortress -but "dwarves" and "complain about all the digging" do not ever meet in a sane sentence.