I stayed at the Arabellla Sheraton and thought it was great. Really good service, lovely spa with free use of pool, steam room and sauna on the 19th floor ^ However with the exception of the view from the window it could have been pretty much anywhere...would rather stay at the Cape Grace, Mount Nelson, 12 Apostles or the ilk next time...
Hotels can be surprisingly pricey in Cape Town, we were quoted almost $800/night for a standard room at the ASGH. As nice as it is it isn't $800 of nice!