I believe there is a big advantage getting larger quantities of cotton patch material and the resulting consistency you get, though others will disagree, and no argument here if things work for you. Problem I find with odd rags and t-shirts is they vary in thickness from piece to piece, some being a tight fit on your jag, others being loose. Not a big deal, but still a bit of a PIA. I find old high thread count bed sheets will provide a nice quantity of consistent material (if you live in a supervised domestic environment you will discover that bedsheets are rotated out and replaced on a regular basis), or you can spend the big bucks ($1-$2 per yard by 56”- 60” wide) on close out cotton flannel, or better yet if you can find it, cotton flannelette. A yard of 60” wide material will give you nearly 240 3” square patches. That is less than a penny a patch if you can find it for $2 per yard. Might end up with some unique colors and patterns on close out, but who cares.
Once you have a quality of cleaning patch material, figure out a patch and jag size. This may mean modifying your jag. Difficult to figure one out without the other. For my use, I take the old high count cotton bed sheets mentioned above and tear them into strips (once you figure out the knit pattern you can consistently tear any width strip you want), typically 1”, 1-1/2”, 2”, 3” and 4”, plus any other sizes I may need. I then mark and cut strips to make square patches and fill one or two clear plastic containers with each size (I believe I am using old 2lb or 3lb rice containers). This gives me an easily visual of my patch inventory. As a FYI, I find that I mostly use 2”x2” followed by 3”x3” patches for most bore cleaning. With a proper jag, a 2”x2” patch can work for me from 45 to 58 caliber. What you use will depend on your jag and patch material thickness. For field use I carry strips of cleaning patch material with notches in it to allow me to easily tear a square patch off the strip (I do the same thing with my roundball shooting patch material for those times I don’t cut at the muzzle) in an attempt to keep things simple, though I must admit, this rambling post likely makes things sound complicated.
Some will suggest using whatever you have. Guess that can work for cleaning and roundball patch material, just don’t get upset when things are too loose or too tight as you randomly use old t-shirts, skivvies, rags or whatever and things don’t work out.