I stayed at the Garni du Centre at least half a dozen times over the past 2 years and I highly recommend it. Although within a short walking distance from the city centre, the hotel is a haven of peace and quietness with an immaculately maintained garden and swimming pool.
The rooms are spacious, with a comfortable bed and simple but effective bathroom. Each room has its private balcony or terrace overlooking the garden.
The breakfast offers all one can wish for, freshly pressed juices, hot croissants, variety of breads, cheeses and cold cuts, or omelette to be eaten on the terrace.
For those wishing to relax or work in the garden, there is a furnished pavilion at the back of the garden, ideal for a quiet read, work (there are power sockets and wifi) or meeting.
I found hotel staff extremely helpful, friendly and ensuring an impeccable maintenance of the premises.
There are many restaurants and bars close by, but if needed the hotel will also prepare lunch or dinner for its guests (order in advance).
Hotels in Kigali are not cheap and I consider the Garni du Centre as good value for money. The only negative point is that it was not possible to pay with a credit card.
I have tried a few other hotels in Kigali, but the Garni is definitely my favourite.