Well, that depends on your taste in adventure.
You can climb Machu Picchu over many days or drive up to a place where you may conduct a one-day walk. Altitude sickness is not a problem when visiting Machu Picchu.
Kilimanjaro offers a variety of pathways to select from, including a day of mountain running or a gradual adventure and acclimatization route that takes 6 to 11 days to lessen the risk of altitude sickness.
You trek up to Macchu Pichu rather than climbing it. It is a moderately challenging trek that is enjoyed by people of all ages. While Kilimanjaro isn’t really a “climb” in the usual sense (depending on the route), its high elevation makes it a more serious endeavor. On Kilimanjaro, the extremes of weather and altitude are more hazardous.
The only way you’ll die trekking to Machu Pichu is if you go off the route in a few perilous places. Kilimanjaro will undoubtedly rank higher on most people’s list of locations to climb in terms of objective hazard and challenge.