I was in Nairobi for 3 nights on business and the client chose the Sarova Stanley. Very good choice.
The hotel has a very british colonial feel to it. Which means you get great service, always very classy, and you feel important.
The hotel staff is very helpful, polite and kind. Rooms are large, with all the necessary amenities. Showers could be more modern though: it was just the old-school shower/bath with a curtain.
The outdoor pool on the fifth floor, surrounded by tables to dine or work is very nice.
I particularly enjoyed the historic feel of the hotel, with many old pictures and stories about former patrons and british colonial lore.
The hotel's main restaurant is very good, but the "à la carte" thai restaurant is by far superior. That is one great restaurant!
The hotel is located in the heart of the city, close to many shops, coffee shops, banks and restaurants.
Wireless internet is free but you have to create a new account every time. Minor annoyance.
It's not cheap though.