As my signature shows, I've been to OKW quite a few times thanks to my
DVC parents. We also stayed at SSR.
OKW is definitely bigger... a lot bigger. Bigger than most apartments bigger. It's the original DVC resort so like most of the original resorts in a particular class (CR, Poly/CB) the rooms are slightly bigger than most later entries in its class (BWV onward, including SSR). Those rooms are tough to beat.
The resort is massive and not centered around a central area. If you live in the South Point area in the back, you really have to drive to get to the Hospitality House. If you decide on OKW request villas in buildings 13,14 or 62. They're all located near the Hospitality House/sandcastle pool and near bus stops.
Obviously the newness of SSR gives it an edge over OKW. I also thought the bus service was better at SSR but this was also in 2004 about a month after the resort opened. It was incomplete so there were only two stops (by the pool and Congress Park) and only about three people were staying in the resort at the time, so the buses were never crowded (I might be exaggerating there).
The only downside of the otherwise fantastic OKW seems to be the bus service. The buses to particular parks seem to take forever to get there and at the parks themselves expect to see at least two (sometimes three) of each other resort's bus go by while waiting for one back to OKW. Keep in mind, this is my experience and I bet there are people who had a fantastic time with the transportation at OKW, but also, I've been to OKW quite a few times and this was almost always the case.
To help ease the frustration, if you do choose OKW, and if you end up near the Hospitality House, always go to the HH bus stop. With the exception of the DTD bus, HH is always the last stop at OKW before heading to the parks so you don't have to sit on the bus for 15 minutes while it travels through the resort to the other far-flung stops. When coming back, get off at the Peninsular stop. It's the first one and it's a short and usually scenic walk back to those buildings near the Hospitality House.
I've already written a novel and I know OKW almost as well as I know the town I currently live in, so I could write more... but I'll spare everyone my rambling.
