I too read these a long time ago, and I too used to have the tattered paperbacks to prove it

. But now I have all the ones I want in e-book, which is much nicer!
My favorites are
Madam, Will You Talk?,
The Moonspinners,
This Rough Magic, and
My Brother Michael. Although
Madam, Will You Talk? is a teeny bit above the others IMO, really, on any given day, my "favorite" could be any one of these. I also like a lot of Stewart's other books, but these four are the ones I reread when I'm in need of some reliable "comfort food" for my brain.