As a babe, don't think it matters, but so you don't have to replace I would get one that is at least 1 in. wide as this fits your hand well and you have a solid grip. The smaller ones can literally cut your hand as the pup grows and may start to pull. Get one that is nylon and comfortable. You will never need one of the 2" ones or I have never needed one this large. I don't like the corded ones, cause they slip. Leather is great, but you must condition the leather, so nylon for me. Dont bother with the run out leads, as this is more for smaller dogs or old seniors unless you have a very dependable dog.
In class we must have a 6 ft, a 10 ft and now 100 ft lead.