You should choose your rope based on intended use.
1. Indoor Climbing
Larger diameter (10mm) with a reinforced sheath for intensive outdoor top roping use
Select rope length according to indoor wall's height and profile
2 colours to choose from to distinguish rope bundles
2. Big Wall Climbing
Larger diameter ropes (10mm) last longer and are safer to use (better braking in the device). They are recommended for beginners. Smaller diameter ropes are lighter and more fluid, but they require higher skill level. Smallest diameter ropes should be used by expert climbers.
Select rope length according to big wall's height and profile
3. Multi Pitch Climbing, Mountaineering And Ice Climbing
Double ropes are used for abseiling after climbing. 2 diameters exist. A thinner rope will be lighter but less durable and its use will require expert belaying technique.
Select rope length according to length of route and abseil
Double ropes come in 2 colours for extra safety
4. Glacier Hiking
A single very thin diameter for lower weight
Select rope length according to the number of persons on the rope : 20m, 30m, 40m