Hilton or Telegrraf ?
There are advantages and disadvantages of being in the middle of the Old Town. Really depends if you want to be in the city or prefer a quieter location with a short walk. The Hilton hotel hasn't been open very long, everything is new and ultra modern. Have a great trip.
There are plenty of quiet places in the Old Town and the new town is no haven of peace. Go for the Old Town, especially if your trip is during the colder months.
As Lusikas said, the Hilton is more convenient if you're by car. However, the Telegraf is in an excellent location for touristing and is a quick walk to all sights in Old Town. I stayed at the Telegraf for a night when it first opened and it was lovely. Never been in the Hilton.
Is there a roof top terrace in the Telegraf to visit for a drink and enjoy the view? Thanks.