My favorite word is the one I'm searching for when I'm snapping my finger mid-sentence.
I've read the contributions of my esteemed 'Plinkers' and I still don't see how a writer can have ONE favorite word. As a child I "read" the dictionary from cover to cover falling in love with several words every few pages; I loved some because of the spelling, some because of the way they rolled off my tongue, others because of the way they were able to convey so much in so few letters. But ultimately I looked forward to using them in sentences where they shone as a result of the supporting words, punctuation etc.
Writers are in the business of stringing words together to capture the imagination of their readers. Most times one word can't have that effect.