No technical climbing skill is required to summit Kilimanjaro, but the route you choose has an outsized effect on how the days actually feel, and more importantly, on your odds of reaching the top comfortably. The variable that matters most isn't distance, it's acclimatization time.
Machame is the most popular route for good reason: strong scenery, solid acclimatization profile, and a reasonable six or seven-day pace. Marangu is shorter and sleeps in huts rather than tents, which appeals to some climbers, but its faster ascent profile gives the body less time to adjust to altitude. Lemosho, the longest of the main routes, offers the best acclimatization and some of the quietest trails on the mountain, at the cost of extra days.
Velvet Trails generally steers first-time climbers toward Machame or Lemosho over Marangu, specifically because summit success correlates more with time spent acclimatizing than with any other single factor. We build in a rest or acclimatization day wherever the route allows it, even when it isn't strictly required.