Another difficult one. I remember so many gardens open under the National Gardens Yellow Book Scheme which were so clearly labours of love and full of delight. I always loved villages where several gardens opened at once - tiny modest ones as well as the Vicarage and the Manor. Whichford Pottery at Shipston-on-Stour was wonderful (part private, part public). They have an interesting website www.whichfordpottery.com and the head gardener's blog is a good infomative read - click on Harriet's Gardening Blog on their home page.
When all is said and done, I suppose my own garden is really my favourite!