The answer to 'best supply line' is that the best supply line for your plumbing needs will depend on the specific requirements of your home and the type of fixture or appliance you are connecting. In general, flexible stainless steel or braided supply lines are considered the best options for most residential plumbing applications.
Flexible stainless steel supply lines are durable, corrosion-resistant, and can withstand high water pressure. They are also easy to install and can be easily routed around tight spaces. Braided supply lines, which have a flexible inner tube surrounded by a braided stainless steel exterior, are also a popular choice as they provide similar benefits to stainless steel lines while being more affordable.