I have stayed at both, and the Doubletree Suites (the one in Anaheim on South Harbor, not the one in Orange) is much better. As a hotel it is so much nicer, and the beds are SO comfortable at the Doubletree. It feels like more of a "hotel" to me, too.
We always get the free breakfast buffet because my husband is a Hilton Honors member due to work travel. The buffet is outstanding--it is like a beautiful brunch buffet with all that you would expect with that. Eggs, sausage, bacon, ham, omlettes, homemade granola, fruit, berries, bagels, breads, pastries, cereals, coffee, juice, milk, and stealcut oatmeal with all the fixings. We get free buffet tickets for each person in our group. My husband doesn't go with us-but we put his name on the reservation to get his Hilton Honors benefits. We also get free wi-fi with this. We always get a suite on his points (so we don't end up paying for the room usually)--and have always been given the top floor with a fireworks veiw per our request. It is such a quiet hotel, too--you can't hear any of your neighbors at all. This wasn't true at the Embassy Suites, unfortunately. The beds are so comfortable that I actually look forward to sleeping on them. That is a first for me in a hotel room! I have stayed in some pretty nice hotels over the years, but this one is really great.
We had been spoiled by always staying at one of the DLR properties over the years, and I remember thinking I wasn't going to like the Doubletree Suites very much--but I loved that our stay was going to be paid with my husband's points. I was so pleasantly surprised by how NICE and lovely our stay was there. We have stayed there our last 3 trips, and plan to again in December--so that is how much we like it!
If you look at the reviews on tripadvisor.com, it is always rated way up there (like int the top 3) for the best hotels in Anaheim--and I can see why.