I like Efina from Wonderfil a lot. I'm using it for hand piecing right now, but it's also a wonderful option for hand appliqué.
Efina was developed for hand appliqué. It is a 60wt 2-ply 100% Egyptian Cotton, made exclusively from the highest calibre extra-long staple Egyptian Cotton. Efina is strong thread that is uniform in diameter (no lumps or bumps) with a visible twist.
Buy individual spools for by the set.