By the way. If anybody knows how to design a garbage chute that accepts sentient corpses, but not dwarves.
I don't think this can be automated. At least not without DFHack type tricks.
Or at least how to get dwarves to prefer coffins over the garbage chute, I'd much appreciate it!
It can be done in vanilla with a quantum stockpile-like setup. (Corpse+refuse stockpile, feeding a stationary minecart on a track stop set to dump, on a route with only one stop, where it's always loaded, feeding from that pile, with the dump tile over the mouth of the chute.) If that's what you're doing, simply forbid sentient corpses from the stockpile that feeds it, or at least those of your dwarves. (Stockpile settings, which I think is q->t.)
If you're manually dumping your dwarves & other corpses with k->d (or d->b->d)...then don't, and make a setup like what I described
Garbage dump zones are indiscriminate of what's being dumped; once marked as junk, it's all junk; they can't be filtered except by not designating what you don't want to be dumped.
With corpse stockpiles vs. coffins, I think I've seen it happen both ways (to the pile first, then the coffin, vs. directly to the coffin), so it might be best to take the precaution of only allowing non-sentient corpses in your garbage-feeding stockpile.
As far as my own burial practices, I definitely try for a nice mausoleum, somewhere in a good stone layer. Often I have efficiently-packed, long hallways with 1x1 alcoves on both sides housing a combination of (stone) coffins, statues, and memorial slabs according to some kind of pattern, the walls engraved. This time I'm trying a multi-layer, broad hall with large columns (think Moria), with walkway-accessible coffin alcoves as above lining the walls. We have...a bit of a necromancer problem at the moment; he left about 60 well-armed undead outside, and we've been turtling (cut off from the mausoleum, actually) ever since (the necromancers themselves left a while ago, but we're still officially under siege, as well as de facto.) But the visitors...dear Armok, nearly 300 visitors have died since the undead showed up. They just enter the map and get slaughtered...despite our low food supplies (roleplaying with no underground crops), we built tunnels to try to rescue some of the more useful ones from the edge of the map to start a resistance force, with some success. But there are still over 300 corpses topside, which, when the next necromancers come...
So yeah, basically, even though I don't usually use garbage chutes, I think I'll have to this time