The Marangu (the “Coca-Cola” route) is considered the easiest route out of all the routes to the summit. This is the only route where the nights will be spent in huts instead of tents. The Machame (the “Whiskey-route”) route is similar to the Marangu route in terms of difficulty. This would be the second easiest. The names Coca-Cola and Whiskey came from a long time ago when the difference between the two routes was way bigger. Nowadays one is not way easier than the other.
If you prefer to sleep in huts and don’t mind to take the same route up as well as down, then your pick would be the Marangu route. If you prefer to sleep in tents or have two different routes up and down, Machame is the better option. Other options (all with tents) are Lemosho en Rongai (both a little bit more difficult than Machame and Marangu) and Umbwe (the most difficult route).
For certain routes, it is possible to climb to the summit via the so-called “Western Breach”. This route is more difficult but mainly more dangerous.