I don't know if you had actually been there but Hilton is located in the most crowded part of the city in the TOP center,its 100 meters away from "Vitoshka" str. wich is Sofia's "la Rambla"!
A super place to stay. Top service as you would expect from the Hilton Group.
It was definitely the quality you'd expect from the Hilton name - beautiful room, coffee-making facilities and great big bathroom. It's not exactly in the centre so that's the only "complaint" really, but still able to get anywhere by taxis or bus.