The Rongai, Shira, Lemosho, and Machame routes are camping routes that take longer and are considered more scenic than the Marangu. On the Marangu route, you will be staying in huts as opposed to camping, and you hike up and down the same path.
The Rongai route takes you up the north side of the mountain and you descend down the Marangu route. The Lemosho and the Machame routes traverse the mountain and descend down the Mweka Gate.
The Shira route takes you on the far west side, and is essentially the same as the Machame route, though you start at a higher altitude, which gives a good amount of time for acclimatisation.
How many days are the Rongai, Machame, Shira, Lemosho, and Marangu routes?
The Rongai and Shira routes both entail 6 days on the mountain while the Machame route has two options, a 6-day hike and a 7-day hike.
For those that need extra time to adjust to the altitude, the Lemosho route is best, with 8 days total on the mountain.
The Marangu route is the shortest route at a total of 5 days on the mountain. If you are concerned about altitude sickness, it is best to go with a minimum 6-day hike, give yourself enough time to acclimatize. It can make the difference between summiting or not.