As a So. Cal. resident, I can say January is sort of hard to predict (as is any time from October-April). It's been rather dry and hot the last few years (pictures of me in tank tops for my late-December birthday). But, the weather people are predicting a super El Nino, which usually translates to tons of rain, so even if it's 65-70 degrees outside, it feels colder with rain. I have gone in the winter where I've been bundled up in 3 or 4 layers and still freezing and I've been where I'm sweating to death in a tank top and shorts. Best bet is to watch the weather as your trip gets closer. It looks from your profile like you're in Colorado and I know a lot of people from the colder parts of the country find southern California warm even when we're all bundled up. So, it's all relative. The rain is really more the determining factor. We're suppose to get a ton of it this January (in theory at least), so I'd probably recommend booking PPH. The pool at PPH is fairly nice anyway and has a water slide, so on the off chance the rain doesn't come through for us, you'll still have a good pool, even if it's not as good at DLH.