The Sheraton is great! It is about a 15-20 minute walk from the Serena. The Serena is supposedly a nice place but honestly I thought the Sheraton was fine. The Serena is better located for a Mzungo-oriented shopping center (with an overpriced Uchimi supermarket) and the Sheraton is slightly better for access to the town center and embassy district.

I don't know of any other international chains- there are some Kenyan chains in Entebbee.