I bought one of the original 7700'sand the only thread it hates is the Sulky metallic (though Sulky in general is also problematic sometimes). I have used C&C and some colors break but most works well. I use poly, poly cotton, cotton, metallic and rayon. I use both Organ and Schmetz needles -- I have heard the Schmetz are a tiny bit shorter but I haven't had an issue. What is more important is the type and size of the needle -- and Superior has a chart that tells you what needle with what thread weight & type. I sew slower with metallic. (Superior needles are also Organ -- as are Janome needles). Make sure you get the correct bobbins for the 7700 -- you need Class 15 or A bobbin and a lot of the prewound bobbins are L which are not as deep as the A bobbins.