You know your pet best! Some will wear whatever you'd like without a care, others may be bothered by hardware or collars. At Kite & Anchor we try to have a little something for everyone.
My recommendations for dogs who prefer something lightweight are the 1/2" and 5/8" widths, we would also suggest the plated hardware choices over the stainless and brass because they are heavier than their plated counterparts.
For large dogs, the heaviest weight hardware we have include solid brass and stainless steel. I would suggest bolt clasps for strength if you've got a large dog that pulls a lot.
Lastly, when wearing a the hands-free leash, especially the quad, typically the most comfortable choice is 3/4".