My all-time favourite...not sure but probably one of Alvin Langdon Coburn's vortiscope images or Lewis Hine's Cotton Mill Girl but like music it will change with my mood.
There are some excellent photos posted on 28DL (there's far more rubbish....but it's not a 'photogrpahy' buletin board) and they'll be my favourite for a short time too.
In terms of my own photos then my favourite is likely to be something taken within the last few weeks (at any given time) and several have made it onto here. There are others which will always be amongst my favourites but for various reasons I won't post them on here.
Enough waffling though...here's one that was in my favourite list and related to the BB. I don't expect it to have wide appeal but why should it? My photos are for me even if I do sometimes allow others a glimpse through my eyes.