I hate the looks of nylon tack. It doesn't clean well, if you need to punch holes it always seems to be messy, & they just don't seem to fit right. I also just think it looks tacky... Personal opinion.
For everyday casual use I like biothane. A few of the members raving about it here actually spiked my interest on the products. Then I got to actually put my hands on some at the horse fair - I like it. You can tell it's not leather, but for casual use with easy cleaning - I'm all for that LOL. Plus it comes in cool colors like nylon without looking nasty.
I still love my leather the most, but if I couldn't afford it or didn't want to ruin it I would go biothane. I'm actually looking into some halters & bridles.