Original post from June, so maybe too late here.
We stayed at the Sheraton several times before the LL Hotel was built. It has a private entrance (15 min walk) to LEGOLAND.. it's neat because it drops you into the back of the park, so hopefully you can hit rides back there before the early entry crowd that went in at the front, gets back there. Besides that, it's a typical Sheraton... not themed to
LEGO in any way.
The LEGOLAND hotel, on the other hand, is so much fun. If you have kids in the 4-10 year-old range then it's perfect for you. There are LEGO bricks everywhere... play structures in the lobby... castle, stories, early park entry... treasure hunt in your room which is decked out in a LEGO theme. Some things will amaze you but I don't want to give it all away because the first time we experienced some of them they were so neat, it wouldn't be as good to go in looking for them. Just... Stay there. Hopefully you've seen the LEGO movie, as there are subtle jokes that tie back to it. It's as expensive as a Disney Deluxe, but with as many amenities and immersion as a Disney Deluxe so it's worth it. You do get a breakfast buffet with your stay... and it's not your typical Sheraton "muffins and juice" buffet... it is a real buffet. The dinner buffet is even better, but you have to pay extra for it and it's on par price-wise with a Disney character meal.
You can do LEGOLAND in 6 hours or less, especially the Florida one which is not crowded. The California park is usually packed. LEGOLAND Cali does have a water park and a small aquarium on the same property, so you could make it 2 days and it would be great!
I would not recommend staying by Magic Mountain, since you'd be looking at a 2-3 hour drive to/from LEGOLAND. If you hit the morning rush, crossing LA like this would be a terrible start to the day.
Warning: The LEGOLAND Hotel is packed with kids running around everywhere. If you are going for quiet or relaxing, this will not be the place!! Altho... there is a full service bar.