OKW - bigger rooms which could make a big difference if you're talking about a studio versus a 1BR or bigger; studios have 2 queen beds (or did that change with the refurb?); quieter resort; the on-site sit-down restaurant (Olivia's) serves all 3 meals; the counter-service restaurant (Good's Food To Go) seems to have really limited indoor seating; 1 big pool and 3 smaller quiet pools. I don't think there's an interactive water-play area there but I could be wrong.
SSR - rooms are smaller (though studios are still bigger than value or mod rooms...or BLT studios for that matter); the on-site sit-down restaurant (Turf Club) only serves dinner but the food court (Artist's Palette) is bigger, much bigger indoor seating, and because you're closer to DS it's that much easier to have other dining options (some, depending on where your room is) are easily within a 10 minute walking distance, maybe even 5 depending on how fast your party moves). 2 big themed pools, each with an interactive water-play area and (I think) 4 quiet pools. There is the on-site spa if you're into that sort of thing.
Both resorts have bike rentals, arcades (I think OKW has 2), physical fitness centers, bars/lounges.
This isn't make or break, but one cool thing about Artist's Palette is that the souvenir shop is combined to it, so you have things to look at while waiting for your food to be ready. I'm sure other people find it an inconvenience to have looky-loos so close to where you're eating.
Pretty sure both main pools at SSR are bigger than OKW's big pool.
I've not stayed at OKW, but I have stayed at SSR a few times and it's my home resort. I think if what I wanted is a low key trip with lots of down time, where I know I'll spend ample time in the room itself, I might opt for OKW. But I really like SSR, I like being that close to Disney Springs (even if the relatively new "Preferred" Location category makes it a PITA to stay at Congress Park). Neither resot is as elaborately themed in that magical whimsical Disney way as other DVC resorts like Wilderness or Boardwalk, but they're very nice and I had no complaints my times spent at SSR.