I've heard horror stories of people generating dozens of worlds, scanning them all looking for That One Site With Everything Just So and spending literally days not playing, but looking at the embark screen.
BTDTstillhuntingforTT-S
I've recently been looking for a perfectly flat (i.e. fully zeros on the slope-indicating map) site with shallow and deep metals (though not too bothered about which, I'll work around that[1]), no river, no aquifer (I'll get my water from the caverns), as much soil as possible[2], and fiddling with various evilness/wildness settings to taste.
This is for a fort design that my 5yo original .25 fortress could well have been, being all the above except with a river running through it to spoil the symmetry. (That one I'll continue.)
On the machine at home, I ended up on an EVULZ snowy waste (loads of zombie things, both on the surface and in the caverns, although occasionally some non-zombie elks and reindeer wander by, which later on I'll be able to trap) and a intrusion of aquifer into the SW corner that I'm currently working around, and I've just plumped for one here at work (*cough*) that's actually serene wilderness but again snowy waste (actually ice-block, most of the ground) although it has a freezing forest in the SE corner, so at least I'll get some wood right from the beginning (as opposed to relying on trading until caverns spawn underground trees into the little underground soil that I can easily get into). I also had a yeti on that map, on embark[3], which I suspect I need to deal with quickly, or hope moves away. (It's been a while since I embarked upon a freezing/glacial site, my memory is hazy as to what yetii are like, or indeed if I ever met any way back then...)
[1] Although the various iron ores would be nice, and are so far absent.
[2] In the end, although the soil was given a Finder option of "loads" I ended up getting at most one layer, and the surface being snow-covered, on the results mentioned further down the above...
[3] The home map has been played for a year, the Original Seven had only been augmented by four additional immigrants in the early days (very little attractive architecture) but the very next wave shoved me up to 37 of the blighters and a whole lot of pets/tame wildlife, non of which (thankfully) are overly greedy grazers since I've only got some of my dug-out soil rooms old enough to have decent amount of grass-analogue on their floors.