For piecing, I use Connecting Threads. For machine quilting I use Glide. I love, love LOVE Glide thread... no lint and it quilts absolutely beautifully. Both are economical and Connecting Threads tends to run sales. I buy their white, off white and black on the cones for piecing. I do have a few of their color sets for when I need something other than the basics and it has served me well.
It also depends on your budget too. I no longer use serger thread - I was told the same thing, that it was okay to use, and I have found it really just doesn't stand up and it breaks too often when I machine quilt.