Mine is easy, it is the one that got away...
I had a Bianchi Sport SX in the 80s, loved the bike, did a lot of impromptu racing in high park and on some of the trails around Toronto. I sold it when I had a kid and stopped having time to ride a lot.
But even as a Bianchi owner, I was also aware I had the best of the Japanese frames, and wanted a celeste Italian made Bianchi, preferably with Italian components. I've never ridden a Campy equipped bike. I'm sure the reality may not live up to the dream, but there it is.
When I was riding a lot, I was a strong 170 lbs, 6' rider. I'm much older and slower and heavier, so I'm not sure an SL Columbus bike would be appropriate. Even back then I was thinking SLX.
Not long after I joined the forum, Bianchigirl was dealing a CDI, I have the feeling I should have jumped on that.
One of the members here did donate a Bianchi frame to me, a BICI II that I am still planning to build up with an old Shimano 600 group; triple crank, long cage non-SIS RD.I plan on wider tires and making it into a more comfortable bike.
So I keep looking....someday one will fall in my lap.