No, you should use neither. If you follow Talbot's original notes you will see this was not used with his salt prints. As soon as you use fixer with a salt print you destroy the original colour. What you need to do is take a large saucepan of water and bring it to the boil. At the same time you keep pouring in as much salt (NaCl common salt) as will dissolve. What you are making is a super saturation salt solution. When no more dissolves, you let the solution cool. Bottle this and after exposure of your salt print pour this over the image. This will stabilise the salt print, but not fix it (having said this, I and Talbot have noticed that if you get the proportion of salt ratio in balance with the silver nitrate solution coated on the paper, it will be quite permanent, but this is a different story we won’t go into here and one I can't do it consistently). You then need to scan it when dry before the image deteriorates.