For me, I always buy alternative sexy costume for heroine and/or NPC girls.

I was just gonna say the opposite. :P

Cosmetic is not really a big draw for me. I want added levels/missions regardless of how simple or unpolished they are. A great example of this is all the fan made DLCs for AoE2. Most of them are awful, but they are still new; new maps/new missions; so I was very happy with them.

No kind of DLC is a blanket must-buy. Least of all chainmail bikini DLCs for Pervy McPervmeister.

None. Screw DLCs, give me proper expansions/addons.

Shivering Iles is a good example.

(Good) story DLCs or expansions, maybe soundtracks or art books occasionally.
But most of the time I just wait for some "GOTY" edition to get released, don't care about cosmetic stuff or "cheat supplies" like in game XP/money or better weapons

I have a few criterias for the DLC i buy.

1. It must be to a game i like to play.
2. it must add something worthwhile to the game through content, redesigns for better and other enhancements.
3. It must be worth it's price or it's a buy on sale.

Costume, weapon, portrait packs and other cosmetic stuff can fuck off and as much as i like Falcom games they are one of the developers guilty of putting out shitty and poorly priced cosmetic dlc's, Beamdog too but unlike Falcom i hate everything about them.

The kind that already comes with the game.

On a lesser matter of jokeposting, I suppose my preferred DLC is the classical expansion pack. More missions, more units, more tools.

Additional chapters/clans/quests/areas...

Something that tells a new story in the same game world from the point of view of a different character.

Cheeeeeeeep, but seriously I usually get them all at some stage and price is no problem.

if its a game I adore then I get them cuz im addicted to the game and want to keep up with my mates. In the past when i used to play microtransaction games I would get the ones that appealed to me, usually nicely done mounts were my weakness or decorating cosmetics. yah, i did that... hence why I no longer play those kinds of games.

This. I wouldn't completely rule out buying cosmetic stuff and other minor DLCs but they'd have to fulfill these conditions, too.

Basically, DLCs that add interesting new game modes or levels. Never buy alternate skins/costumes DLCs.

I also buy some DLCs that give extra goodies, like comics or artbooks.

All I can get from buying a GotY/Collector's/Complete Edition long after the game's original release. I rarely ever by DLCs separately.