For piecing I use
75/11 or 80/12 because I use thin thread for piecing, usually 50 2 ply or higher. For any thread that is 50wt 3 ply or 40 I use 90/14. Topstitch needles are the type I use the most. Singer needles are the best for FW and vintage Singer machines. The are a teeny tiny bit different is length.