Swiss flights to NBO/ DAR are in their newer airplanes with the new layout in business (stacked alternately with 1-2-1/ 2-2-1 seats). Same as AY's new business class. Great seat, great food, great service, much smoother transfer in ZRH. Much as I like BA, I'd say if you are otherwise indifferent between the two airlines take the Swiss option.

Precision is fine.

If you're staying overnight in NBO then the Serena is your best option.