It would have to be my Explosif of course, simply because I've owned it for so long (I bought it s/h when it was about nine months old) - riding it (or even just looking at it !) brings back so many memories of great rides and race days with so many good friends that even if I was no longer able to ride it I would keep it for that fact alone.
Even while I'm typing this I can still remember so many good times that it's been a part of that I know I simply could not bring myself to sell it.
I am however an overly sentimental old fool, but that being the case I really don't care either....