'Land' is her classic work and contains most of the images you'll be familiar with. Very quiet photographs and a book I find myself coming back to again and again. A very important photographer, in Britain at least.
I bought 'Our Forbidden Land' first and was quite disappointed. The book is politically & environmentally motivated, opening with some contradictory quotes from Margaret Thatcher - before my time, but I believe this was commonplace. The images in the book only serve to support (and I should emphasise this) a quite bloated and difficult text regarding access to the British countryside. More for those interested in the history of the countryside and walking, than studying photographers. I've kept hold of it hoping it may hold some relevance for me and my photography in the future. It certainly is an impassioned piece of work, but Land has the best selection of photographs.