Favorite Companion book?

I like the Magic Realist books...
I also like the Shining Tribe book as well as the Haindl books (both Rachel Pollack)
....oh and the Druidcraft book. It has very understandable courts, and it arranges the minors by number rather than suit.

My favorite companion book is Karen Mahony's companion to the Tarot of Prague. When I was a still a tarot "newbie" I found her book to be an excellent, insightful, and original guide to tarot in general, and not just strictly the Prague deck.

My second-most favorite companion book is the one with the Druidcraft.

I must remember to buy the Tarot of Prague kit. I loved her BBC.

The Victorian Romantic companion book is awesome and so are the Fey, BBC, and Druidcraft. These are the ones I've read till now and really enjoyed reading them.

Tarot of Timeless Truth (I've often used this book with other decks)
Druidcraft
Fey

Bodhran

The Magic Realist Press books
Druidcraft
Halloween
Russian St. Petersburg
Ship of Fools
Medieval Enchantment

and a bunch that come with oracles, too. I really do find I learn something valuable from basically all the companion books, when I get around to reading them!

I've just been reading the companion book to the Victorian Romantic and I'm impressed. Very nuanced and sensible, describing different approaches to tarot and encouraging the reader to find his own way. Very thorough and concise, and a lot of atmosphere, with a short introduction to the victorian era, some of the original engravings and literary quotes and such.

I have to disagree about the Druidcraft though. The approach is great, grouping the minors by number instead of suit. But I find the actual explanations very vague and confusing. But then I think I find all the changes they've made to the majors very vague. I can work quite well with the deck, but for me the companion book is just too ... new agey?

Some excellent and in-depth companion books:

Tarot of the Spirit, by Pamela Eakins

Renaissance Tarot, by Brian Williams

Pythagorean Tarot, by John Opsopaus (and it is even online!)

And one of the classics:
The Book of Thoth, by Aleister Crowley

The Enchanted Tarot by Amy Zerner and Monte Farber.

Definitely the Victorian Romantic.