The Wifi seemed pretty fast at the LAX Hilton last week when I was there and also is fast at the WIT DT in Chicago and the Miami Bently.
Properties I have noticed it the slowest at is Trafalgar in London (I was there the week before the olympics and was told it was going to be upgraded in time for the olympics and there are others who have complained on FT and TA about how slow it is) and it also seems really slow at the Palmer house in Chicago but it is a large hotel and they give silvers free wifi if they ask so that doesn't help