I love Connecting Threads 50wt cotton or the even thinner generic poly serger thread best for piecing. www.connectingthreads.com
My favorites for machine quilting are the Rainbows (poly) and King Tut (cotton) lines by Superior Threads, and I love any of Thread Art's 40wt embroidery threads, too. Their prices won't make you keel over in sticker shock, either - I've never had it act up in any machine, from my 1894 Singer to my Futura embroidery machine.
I just got some YLI Soft Touch 60wt for hand applique from Heirlooms Forever and it's SUPER nice, but I like the finished appearance of Bottom Line from Superior for hand applique better than anything else I've tried. Superior So Fine and YLI Soft Touch behave better, but Bottom Line is invisible or darn close to invisible. YLI Silk is invisible or nearly so, but it's a pain in the neck to handle, especially to anchor.
Soft Touch - silk finish 60wt cotton:
http://www.sews.com/notions/threads/...softtouch.html
Bottom Line by Superior:
http://www.superiorthreads.com/shop/...e/description/