Many yoga towels are made from super absorbent microfiber, which is why they are so great to use during a hot yoga practice. They absorb the sweat that would otherwise puddle on your mat creating a very slippery situation. Some towels have a rubber or silicone layer or dots on one side to make them more slip-resistant from the beginning of your practice, but since microfiber doesn't become grippy until after it's wet, it is recommended to spritz your towel with water before you get started either way.
So outside of the nubs or rubber-like texture on some towels, size is the biggest difference from yoga towel to yoga towel.
Here's a quick size comparison of the towels we sell:
When purchasing a new yoga towel, consider how much coverage you need.
If you want a mat-size towel, than try to match a towel to the size of your mat for true full-coverage during your practice.