Have not stayed at the Doubletree Guest Suites but know of its location, which is above the #10 Freeway and on Fourth Street (a busy thoroughfare). Not sure if noise would be a factor as a result. Don't think you will get much of a view. If you're walking, you will find it easier to get to the 3rd Street Promenade from the Doubletree and it is also somewhat closer to the Santa Monica Pier. On the other hand the Venice Beach area is closer to the Delphina and its location at the edge of a residential area in Santa Monica is also something I appreciate. If you don't plan to do much walking the location of either is probably not that significant. I would probably prefer the Delphina, especially with an ocean view room at the back of the hotel because of the view and quiet. Also parking at the Delphina has traditionally been complimentary, which in LA can be a significant cost otherwise. The Doubletree is an all suite hotel so if this is important you may wish to look more closely there. My understanding is that the rooms at the Doubletree may be in need of an upgrade or redate whereas the rooms at the Sheraton, as well as all their public areas, have recently been updated. Also don't forget that the Dephina has Sheraton Sweet Sleeper Beds. Not sure what the bed situation is at the Doubletree. Have always been treated exceptionally well by the staff at the Delphina, cannot say enough about there professionalism, friendliness and attitude.

In summary you may wish to run both these properties on tripadvisor.com and review some of the comments there. I know that they are both rated within the high middle range of the hotels in Santa Monica.