I also haven't been going for "most efficient," I just go with what I like and have developed over time, although I try to shave things a bit here and there to make them more effecient, gradually.
Outside: Any pastures until I get underground pastures dug out/the caverns breached for spore propogation. Plus a small refuse dump (with the useful "refuse" forbidden) and garbage dump near the entrance, for use until I get the underground ones made. I used to put my aboveground farms and my bee hives out there too, but have recently started digging out areas for them, channeling out on top, and making sure there are no ramps left leading between the outside and the farm area. I link it directly to where my troops muster for invasions, and trap the hallway.
Entry level: One main entrance hall, trapped (eventually) to hell and back, and doors on either end. Beyond that is the area where my troops are stationed for an outside-level invasion, with the stairs leading down into the rest of my fortress. As mentioned I've also been putting my "outside" farm on this level, as well as the beehives. I also include a Trading Depot on this level, in a burrowed-out space with a three-tile-wide access that can be shut by a drawbridge, and it also has access to the rest of the fortress, usually via the troop-muster-area just to be safe. A stockpile for crafts is below it, since those are generally just for trading purposes.
The next few levels are dedicated to farming and ranching. I usually put one big central room around the stairs leading up and down, which has my farming workshops, querns, screw press, butchers and tanners, and one craftsdwarf shop and leather shop. Around this are a few stockpiles for leather, tools, bones, animal corpses (behind doors), etc., to keep them close to the workshops that use them. I usually put my underground farm on this level as well, in some area that has soil, with stockpiles across the hall that hold some of the plants (the ones that need milled, processed, etc.), and seeds. Also on the first few levels are pastures, depending on what areas have soil, how much space I have to work with, etc. Of course, getting these up and running requires the caverns to be breached. The lowermost "farming" level, where it often is at least partly rocky, is usually dedicated to my "bird" pastures - the stuff that doesn't need to graze, but does need nesting boxes to reproduce/produce tasty tasty eggs. Each pasture has doors on its access points so that I can lock the birds in and keep the eggs from being disturbed, if need be. I aim to eventually have each bird species in its own pasture. (Usually 20x20 spaces.)
Right below the farming area is my military level. One barracks for each squad, with beds, weapon rack, armor rack, and archery target. As well as a cabinet and chest, although I don't think they actually get used. (More for the flavor, I guess.) Those are off to the right, along with a central stockpile zone for backpacks, quivers, and flasks, to keep an eye on how many I have/need. To the left is the bedroom, dining area, and "office" of my sheriff/captain of the guard. The office is actually pretty big, and includes jail cells, restraints, etc. In the center of the level, I have an animal training zone to the north of the stairs, and to the south a kennel, with my animal stockpile to the south of that.
Next is my working area, with my general workshops and stockpiles (both for materials, and finished products).
Below that is my living area - my main dining room to the right along with kitchens and main food/drink stockpiles, to the left, my hospital, chief dwarf's room/office/etc. (yeah, they don't need an office technically, but he gets one!), and well. Oh, and a dormitory for use until I get all the bedrooms up and running. Speaking of which, the bedrooms also go into this level, all around the centralized area that I've already mentioned. There are four hallways leading in the four main directions from the stairs, and at the first intersection for each of them, I have a dwarven bath filled with level 2-3 water, so dwarves going through end up washing contaminants off themselves.
The next level, as expected, is dedicated to a water system. A tank to hold the water that I drain off from a river/brook (or sometimes just murky pools, but I usually try to embark on running water), with channels to the cistern for my hospital well, and each of the four baths (which go down into this level, since they're channeled from the level above). A number of floodgates and levers are involved.
Below the water system is my office area, and theoretically my throne room for whenever I manage to get the king and his retinue. Pretty much what it says on the tin: bedrooms, offices, and dining areas for my nobles.
Next is my leisure zone: a level with a communal statue garden to the north, to the south a zoo (with built cages of wild animals and hostiles I've caught), to the right is the aquarium (with, well, aquariums built in it, holding various live fish I have my fisherdwarves catch.) The zoo and aquarium are marked as meeting areas, so that the dwarves can hang out pretty much all through the level when they have free time.
Next is the burial zone. One big graveyard with built coffins for common dwarves and pets, with some spaces left for memorial slabs if I need them. To the right I eventually build tombs for my military captains, with tombs to the left for my nobles. There's also a corpse stockpile behind doors, for if burials are backed up for whatever reason. (Read: siege out-killing my prepared coffins, etc.)
Below the burial is, well, the trash level. An indoor garbage dump to the north, another refuse pile for non-useful refuse to the south, both behind doors.
The next level is a secondary dining room, with more kitchens/stills. Below that is my arena, where I get rid of any extra hostiles/wild animals and train my military all in one swoop. The dining hall above it has parts of the floor channeled out, for the dwarves' viewing pleasure.
That's pretty much all I have so far, except eventually for some magma furnaces/etc. if and when I reach the magma sea, since I haven't experimented yet with pumping magma up to the main fortress. I really do need to do that at some point.