For me it has to be the articulation...And how the body looks overall. I honestly have a hard time buying anything other then Obitsu's! I haven't met a doll I loved more then an Obitsu besides other ABS dolls. I've been spoiled by them so to speak. My tiny is an Obitsu my 1/6th is an obitsu if I EVER managed to get enough money for an MSD or an SD...Yep quite possibly they'll be an Obitsu too. XD;; I love how well they pose. I haven't met a doll that can pose like an Obitsu can to me or feel like the Obitsu ABS. I like Volks dolls too but I just can't stand the lack of certain joints. XD Maybe it's cause that was my first doll and it's sort of a safe zone for me...I love resin too it's beautiful to see all the different dolls, sizes and models but the price tag is what keeps me sort of in my little 'zone'. XD My parents don't even freak out anymore when I wanna get an Obitsu that's like thirty bucks but 105 was even getting a little 'pricy' for a Dal I'm now selling.
The face also is an important thing. If I don't like owner pictures or fall in love with it right off the bat I'll probably never like it. Ironically I used to be really creeped out by Nano-Haruka's...They always looked so angry in some pictures but after seeing different styled face ups on them...I fell in love. XD And after seeing a Nano-Gretel blank? Sold!
Sorry I didn't mean to ramble. XD;;