My experience with nylon straps is that they wear down and fray apart. One snapped when I was going up a hill and while it didn't ruin my day it was annoying enough for me not to want to use them again. I'm riding with fake leather straps and they're holding up really well, BUT, they do come loose a lot. If I'm going anywhere farther than my commute to work I need to tighten them or else they're practically useless. Regular tightenings every week.