I really like isacord or anything made by superior for FMQ

Isacord and Aurafil are my "go to" FMQ threads. Unfortunately, I have only been able to buy Isacord online.

I use either Superior's 50 wt. So Fine or 40 wt. King Tut.

I like using Glide thread. It has a nice sheen and the tension on both sides is beautiful.

I use floriani poly embroidery thread often. It quilts beautifully and has a pretty sheen. It is also very strong.

If you're going to want a lot of stitches. you can try a 'bottom line' or 'decobob' or Wonderfil Invisifil in the bobbin and on top, but you have to experiment to get the right needle! I'm using Jeans 70/10 after trying a lot of needles.

I like Aurifil 50 for piecing but I also use it for FMQ along with Aurifil 40 weight.

A lot depends on your machine as some machine are persnickety about the kind of thread they like. Mine absolutely WILL NOT sew with Coats & CLark Dual Duty. Anything 40 weight should show up nicely - contrasting color will show even more. Cotton will be more linty. Polyester will not leave lint. Try a few different brands and see what works.