I've never used nylon, (I don't think I have anyway.) I can tell you that I have had holes fail before the cord, but over years of hard wear...think saddles and such, linen has been known for dry rotting. I'm pretty sure nylon won't rot on you, but for belts, purses, gun rigs etc.., I would use the linen to get the pretty white stitch. As far as needles and awls, nothing special is required, and the diameters are comparable. For most stitching applications 3-cord, and 5 cord are probably the most used. The only other consideration is the twist direction. There is a school of thought about using left (S) or right (Z) twist cord. I use left with no issues. There is a discussion thread on it here somewhere. I bought left for one reason only, and that is because it can be used in a sewing machine. I've never done so, but that was the reason.
Marlon