If you want a nice beach you should go to Phu Quoc, I don't think it's swarmed by tourists... yet. Dalat is a nice place, but as a lot of touristic area, it tend to become a massive souvenir shop. Mass tourism is developping in Vietnam, and it's no pretty. Some places are litteraly zerged by chinese/russians/local tourists and pretty much everywhere this kind of tourism reached, it trashed the area. See Hoi An / Cu Lau Cham / Bana / Nha Trang. It's evolving quickily, some area which were still nice 2 years ago are really disapointing now.
If you go to the north, Ninh Binh is still very nice, and doing some trekking in the northern countryside is nice as well.
As for the hotel, I recommend the Movenpick in Saigon and the Sofitel Plazza (not Metropole) in Hanoi. The Movenpick is a bit over 100 USD a night and the Sofitel a bit under 100 USD a night, but they are really worth it.