Personally I'd say my forts are built around my defense ideals, several vaccum chambers perfected by the use of bridges and z-levels
i.e I dig an appropiate hole into the mountain to let in caravans, ramp up to another z-level where I build a bridge over the hole where nothing can technically break through it even fliers which I plan for as well, not that I have anything more dangerous than an eagle on my map, I just do it, anyway, I repeat this a few times, the last one gets to be the direct entrance into the fort, one before gets the trade depot (AKA drowning chamber) and the one before that is my spindly lane trap detour down some stairs (which has a bridge hanging over it behind a dry moat for sealing purposes) where I keep a long corridor with a ballista at one end behind a fortification observing a 10 tile keep away rule, a fortified drain, then a let in point for water OR magma and behind a corner at the opposite end, a tame animal *preferably a kitten* with an open floodgate for company
Somewhat overkill, but then the only thing I really want to *or possibly can* call the super efficient part of my fort would be my defence, I take no prisoners, unless I get round to building cage traps. Automation is a later development for when my fort is bristling with activity I do keep a military though for the sake of it and emergencies.
Naturally I always look for underground rivers, magma pipes and bottomless pits in my forts for the spice of life =P