Although there is a hotel next to the company we decided to stay 4.4 km further, but more in the city center. A very good choice. We sometimes took a taxi and sometimes we walked. The Marriott is located next to the Republic Square on which you have the statue of Prince Mihailo and is just next to the pedestrian shopping street: Knez Mihailova.
I stayed in room 508 with view on the main street. The isolation of the room is great. I did not hear anything from street noise. The room features 2 separate beds, a desk, flat screen, (on demand filled) mini bar, coffee amenities and a clean and nice bathroom with a great shower.
The breakfast was not booked by default and costs about 14 euro per day. For that you get a buffet with different kind of bread, pastries, cheese, meat, warm dishes, yoghurt, coffee, cereals and many more. There are also 2 chefs that prepare things fresh on demand like American pancakes, omelette and few other options. When ready it is served by a friendly waiter to your table.
The space is not that big, but we always had place and it did not feel crowded. You have few seats with view on the street, nice sitting there.