For people with the time and patience, may I suggest the 'double mountains route.' Start from Nairobi and drive to Nyahururu, preferably using the new Njabini-Dudori road and turning right at Ol Kalou.
From Nyahururu drive to Nyeri town, passing Baks new keja in Mweiga, and turn off to Kerugoya-Embu at Karatina town. Then all the way past Meru round Mount Kenya and through Nanyuki, Karatina, Sagana and back to Nairobi.
You can do it in a leisurely weekend. The scenery is to die for.
"The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth." (Niels Bohr)