You can't miss the Hotel Rila, it is probably the biggest hotel in Borovets and is centrally situated overlooking the mountains. As you come up the road from Samokov, you pass the Hotel Samokov on your left, take the next left and Hotel Rila is in front of you.
The hotel reception is smart and the staff efficient. The rooms are adequate, we had one overlooking the mountain and chair lift. It had a small balcony area which sloped forward (a bit scary didn't fancy falling over the edge from the 6th floor). The beds were very comfortable and the bathroom clean and compact. The room staff were very good and helpful. Food was on a half board basis and was a bit of a scurry as everyone arrived at the start time, thus causing a queue but with a bit of teamwork with other British hotel guests the art of grabbing a table and food can be achieved quite easily. The food it's self is good with a wide selection each meal time of fresh dishes including some Bulgarian specialities such as deep fried cheese (think cheddar rather than brie)- very tasty.
The hotel has a good size swimming pool with two smaller Jacuzzis, one of which doesn't work as well as the other. The showers in the changing rooms are very good and the hotel offers some other spa type facilities for a small charge.
Additionally the hotel has a small minibus which provides a weekly Monday trip to the Samokov markets as well as other trips further afield such as to the Rila Monastery, a stunning must see World Heritage Site (see separate entry). They also run local walking tours but check the distance and how much climbing they are doing, these are steep mountains. Remember Borovets is already at 1300m so it's all up, up and up from here!!!
Overall, a good centrally located place to stay with a range of shops, a bank etc., within the complex.