I'll respectfully disagree with Hitch. Much of what he says is true but his conclusion isn't realistic. Here's what I mean:
If you told us that you wanted a hotel in an area where you could simply RELAX, walk around the area, have a drink at a cafe, great meals, a lovely pool to lay by, I'd say YES! Santa Monica is a great choice as it has great dining and shopping and, of course the beach and the sunsets (of course, we have the sun setting in our neighborhood to -- LOL).
But the fact is: you're not going to STAY IN ONE NEIGHBORHOOD. You're going to move around. You're going to Beverly Hills and Universal Studios and the Farners Market and that means driving to EVERY ATTRACTION you'll be visiting. If you stayed in Santa Monica, then every day, you'll head east (past the attractions you visited the previous days to visit other attractions -- what a waste of time!) If you drive 'into the city' during rush hour, you'll hit traffic. If you wait for it to end, you're shortening your touring day by an hour in the morning and maybe the same in the afternoon.
Yes, central L.A. can be 10 or even 15 degrees hotter than the beach areas but the high temps don't happen every day and when they do, it's not until 11 a.m. or so that it's starts to become significant. By the end of the afternoon, of course, the temps are falling. If you were sitting on the front steps of your hotel all day, you'd feel these temperature swings but since you'll be touring, it doesn't matter where you stay (temperature-wise) because you won't be at your hotel during midday.
In fact, Universal is in one of the hottest neighborhoods in the L.A. metro area and much of it involves being outside queuing up in the sun and the heat (there are shelters from the sun in some places but not in others). The best way to visit Universal is to get there 30 minutes BEFORE it opens so you can be poised to rush in when the gates open. This way, you can minimize the 'long waits in the sun'. If you stayed in Hollywood you'd be 10 minutes from Universal (which you could reach by metro rail). If you were staying in Santa Monica, you'd have a drive of an hour plus the time it would take to 'queue up' to pay for parking, find a space and then transfer (10 minute walk or tram ride) to the entrance to the Park.
Bottom line: you want to be able to get to the attractions in the hottest neighborhoods as soon as possible and you can't do that if you're staying in Santa Monica. Then, on the day you visit Santa Monica, you'll leave your inland hotel before it gets uncomfortably hot (if, in fact, it's going to be excessively hot on that day) and head west to the lovely place that is Santa Monica.
Besides, you'll be able to stay in a much nicer hotel for the same money if you don't stay in Santa Monica.
Hope this helps.