SS gives you a bed plus a sofabed combo whereas OKW gives 2 proper beds so if there are more than 2 of you in the room you might want to consider whether you want to have the hassle of making up the sofabed etc.
OKW also has slightly bigger units than SS so that may be another consideration.
In addition to generally more space in the DVC studios you get a kitchenette. This consists of a 'larder size' fridge that usually has a small freezer size bit at the top (basically good for an ice cube tray). It also has a coffee machine, toaster, microwave & sink. Available on request from Housekeeping are also blenders (cocktails!) and I'm told, kettles though I'd not heard about that till recently so never tried for one of those myself.
Sink comes with a little bottle of washing up liquid, one of those little sponge/scrub washing up things and a teatowel. In the cupboards you get some plastic knives and forks and some paper plate, but glasses and cups are 'real' though cups are those 3 gulp and they're gone type
Umm *thinks* Ironing board, iron and hoover and not sure if they come in normal rooms too but will mention just in case - you get one of those iHome radio/alarm clocks that you can dock and charge your ipod on.
Oh, and obviously you get a patio/balcony.
That's all I can remember off the top of my head - if looking for something specific then ask as I may have just forgotten it!