I like slip leads and martingale leads for just going on single walks or to Flyball or Agility. For group walks, I prefer to have at least one dog on a multi purpose lead so it's one less leash to hold, and the rest are either on slip leads or 4-6ft leather leashes. 1/2" to 5/8" only. And with two exceptions, I only like to use biothane or leather. Unless it's a slip lead, then rope like Mendota (or Zumi) uses is good too. I just hate nylon. And if I am being super picky, I like brass hardware haha. Or at least the hardware has to match whatever collars I am using.