I have both and much much much prefer the Matthews one.
The Ferguson book bases its stories on the mediaeval versions of the Arthurian mythos, therefore including a lot of French influence. It's well-enough written but fairly standard as a guidebook, though with the addition (at least in my copy) of a poem for every Major. The artwork, while pretty, is as LeFanu said rather Hollywoody.
The Matthews book uses earlier Celtic sources of the mythos and feels much more scholarly and mythic. It has a depth to it that the Ferguson just doesn't have. If you buy the anniversary edition (in the green box) — which I highly recommend, by the way, as the card backing is nicer IMO, plus the white border is gone, leaving only that black arch Padma mentioned — then the book combines not only the original guidebook but also a year-long course for working with the cards, previously printed separately. Lots of info and depth in that little tome. And the artwork really does capture the feel of the English countryside. Plus the people are less prettified and the costumes are more historical.
…But I am biased. The Matthews was my first deck ever and it has my heart.