It's interesting that the contemporary Within the Golden Hour is mentioned. When I first saw this thread, my immediate thought was, 'A favorite must be a 19th-century classic, hence my choice of La Sylphide (which is virtually tied with Giselle and Sleeping Beauty and Swan Lake). But why not a mid to late 20th or 21st century ballet?
Because the question can hit you so differently when you resonate with another person whose love of ballet you really feel. Like right now for me I'm feeling what Gianina said -- the way San Francisco Ballet dances "Within the Golden Hour" takes me SO deep into the heart of what I feel ballet is, it's my current heart-throb, the ballet I kinda ache to see again. And that's a kind of favorite, isn't it? It's the one that's been on my mind the most...
Like a lot of non-New Yorkers, I haven't seen enough Balanchine to select one of his; and while I don't think Golden Hour is in that league and certainly it's not a 'great' ballet in the sense of Giselle or many of the others mentioned here, of all the new works I've seen over the past few years of serious ballet-going, it's the one that keeps coming to mind, especially that stunning final image that has been hinted at through the ballet. It may not be an overall favorite, but I'd have to call it a 'new' favorite.
So, thanks Paul and Giannina (and others) for expanding my thinking.