This can be a challenging subject.
Lets see, in my collections I have:
The ones in my sig are keepers:
Motobecane Mirage Sport
Cannondale T700.
My homegrown Long bike.
Solid forked rockhopper.
I also have sitting in the garage:
An older Hard Rock
Another older hard rock that I'm building for a friend. (drop bars ftw).
A Hercules Girls 3-speed.
A columbia 3 speed with chain guard & fenders.
I've thought about reducing my numbers also, but haven't been able to so far.
I don't ride the Motobecane as much now, but it's my first road bike EVER and well, it looks so pretty hanging in my bedroom... I just overhauled it last summer too.
I keep the 3 speeds in case I ever find a shorter girl to go riding with. Columbia for me and the AMF for her. No luck so far. Both need overhauled.
The T700 probably gets the most miles. It's my rain bike (only one with fenders), winter commuter, and sooner or later, my loaded touring bike.
The rockhopper is just getting built up, but I grew up riding MTB's, so I like having a classic one in the collections.
The cannondale and rockhopper have rear racks, but I can't haul $130 worth of groceries home on either one of them. Unlike my long bike.
The hard rock will probably get overhauled into a school commuter for someone, much like the other hard rock.
If I had to go down to just one I'd keep the Cannondale. I just hope I never have to do that.