You should get the yearbook package, it comes with posters!!! Kiss is exok ang hug is exom. I dont think theres much difference apart from the language of the song in the two album.

kiss has the korean version of the songs and a chinese version of wolf while hug has the chinese versions of the songs and a korean version of wolf..i hope my comment makes sense..XD

kiss is exo-k's and hung is exo-m's. not sure what other differences beside that. my sister is definitely buys the kiss ver, now i'm thinking if i should buy the hug, hehe. how about you?

I think the difference is that both (kiss-korean and hug-chinese) versions have two other versions. One with a sticker and the other without one.
Every album has different posters and their covers are different. I'm not sure though. But check out the pictures of the other fans, they already posted those, it might help you.
If I were to choose between both, I'd buy both versions(hug and kiss). :)

I think there isn't necessarily one for each subgroup

there are four versions of xoxo
kiss: Chinese and Korean version
Hug: Chinese and Korean version

I heard they came with different things (poster, etc)