Old Key West & Saratoga Springs are all Disney Vacation Club resorts, as opposed to the other DVC resorts that are Villas within Deluxe resorts). When moderates get oversold, they often offer rooms to people at OKW or SSR instead. Which is not to say they should be considered consolation prizes, quite the opposite. They're beautiful resorts. But the theming is decidedly more muted than at pretty much any other resort on property, and they're a little more isolated than any of the deluxes. And by "isolated" I mean that they're not close to any of the parks though they are boating (and depending on where you stay, walking) distance to Downtown Disney.
Between the three of them, OKW will have the largest rooms. OKW & SSR will have "kitchenettes" - little refrigerators and microwave ovens with a tiny sink for your kitchen-y needs. PO-R will have a refrigerator, which might be tinier than the ones at OKW or SSR, but I could be wrong on that. On the flip side, I believe PO-R's bathroom areas will have his-and-her sinks (though there's no law that says you can't brush teeth or wash your face at the kitchenette's sink).
All 3 of them are ginormous, but I'm pretty sure PO-R will have the most rooms, over 2000 (whereas many of the units at OKW & SSR can house more than 4 people).
I agree that your friend might want to go to allearsnet.com and check out the photos and reviews (written by both contributors to the site AND the readers). There might be one that floats your friend's boat the most. Considering there's a 9-year old in the party, PO-R will hold some allure because of the main pool, "Ol' Man Island," which many people consider to be second only to the Yacht & Beach Club's pool as the best-themed Disney resort pool. But SSR's pool is pretty sweet, too.
If they're not driving, consider this: SSR has an awesome spa (something I bet your friend might enjoy), and if you get on the West Side, you could be walking distance to Disneyquest (which the 9-year old might really appreciate). I've stayed at PO-R and SSR, and have dined at Olivia's and looked around OKW. PO-R is my favorite moderate resort, but I've never seen PO-R's food court NOT crazy. SSR's was almost always not-too-busy when I've gone, PLUS you've got their restaurant which is almost hardly ever busy, AND you're so much closer to all of the restaurants DTD has to offer. And if your friend loves to shop, staying at SSR would probably be a no-brainer.
Finally (and this is based on my admittedly faulty memory), all 3 resorts have main pools and at least a few "quiet pools" without water slides. I know that, when I stayed at SSR, my quiet pool area also had a whirlpool spa next to it. I'm not sure if this means ALL the quiet pools have them, and I don't know if all the quiet pools in PO-R and OKW have spas at their quiet pool areas. I VAGUELY remember there NOT being a whirlpool at the quiet pool area I frequented last time I stayed in PO-R (in the Alligator Bayou section). I'm sure someone will confirm or refute my claim, but if SSR's quiet pools have whirlpool spas and the other's quiet pools don't, that might be a minor-but-contributing factor.
Even if I'm wrong though, I'll say between the 3, SSR would have my vote.
