it really depends what you wanna do. if i were visiting, i'd want to spend as much time as i could near the ocean but that's just me. im from east LA and its totally not worth spending 50% of your time in traffic inland, esp if you're located downtown. downtown is being revitalized but compared to SF or NYC, i don't think the experience is even 1/10th as fun.
kagaya - best shabu shabu you'll ever have. get the banana desert option
getty museum. you can get a 2 for 1 if you hit up the getty villa (not the same as the main getty) and you get the nice shoreline drive on pch. can grab food at malibu farms on the pier off of pch (good food, but really excellent view)
beverly hills - just for your girl really. walk around the fancy shops and whatnot.
venice is more interesting than santa monica imo, but can't go wrong with either. manhattan beach is fun too. more local (pros and cons to this), less touristy. can get an idea of the beach community cliques.
head south toward's the south bay. admiral risty's is a dinner restaurant with an awesome view if you get by the window. alternatively, hit up redondo beach pier and there are plenty of restaurant options there as well. i would recommend checking out one of the korean crab shacks. gotta use a mallet for your crabs but it's fresh af and delicious. rancho palos verdes is super nice to drive through. links at terranea is really nice if you need a place to stay.