I'm actually originally from Los Angeles (technically the San Fernando Valley) and am now living in Seattle! I like that you're doing it backwards. I definitely don't want to end up here. The weather is just killing me (95 degrees one day, pouring rain the next? I just want a normal summer!).
So. I lived there for the first 11 years of my life, and I've gone back at least 2-3 times a year since then. The traffic is shit, I will be honest with you. The 101 is awful, during the appropriate traffic times. And Los Angeles, specifically, can be quite smoggy. BUT I absolutely love the area, aside from those things. The heat is so nice (it doesn't necessarily make you wanna die like it does here), and the culture is so different there. I love Seattle as a city, but all of Los Angeles is like Seattle in the way of city-life. Plus, you can drive to any of the surrounding cities that are aaamazing. Here, everyone drives to Seattle. Haha. I am a huge fan of Santa Monica and Santa Barbara.
I don't know if you drive at all, but one of the things I've noticed (that makes me laugh EVERY TIME) is that Southern Californians have no idea how to drive in the rain. It's ridiculous to watch.
As far as where to live, like I said, I'm from The Valley, so I'd prefer areas like Calabasas or West Hills, but that is just because it's close to where I was raised. I don't know much about West Hollywood.
I hope I helped a little and didn't just ramble!