This article by eveningsends.com is a good introduction to choosing a climbing rope. I found the article because I need to pick up a fresh rope with my upcoming REI dividend and was searching for opinions. I think I am going to pick up a Mammut Tusk 9.8mm 70m because it seems like a general purpose rope that will stand up to plenty of top-roping but is still light enough to take on the irregular alpine outing. I have also had good experiences with Mammut ropes and they’ve built trust in my book. I wasn’t planning on getting a 70m but the article made the good point that as the rope wears I’ll most likely chop off the ends to maximize its lifetime. With a 70m there is more room to chop which is a plus.
One important point that I feel I must reiterate here is that you never want to use a sharpie to mark the middle of your rope. The article says it best.
Finally, don’t use a magic marker to mark the middle of your rope. A report conducted by the UIAA found that using any kind of pen or marker to mark the rope results in a 50 percent decrease in strength! However, another report by Kolin Powick at Black Diamond found that this issue isn’t totally settled.