OFG,
They are all gorgeous....

Assuming that they are all in good tune... If you have a nice quiet spot nearby where there aren't many people, you can take each one and open it up/let it rip going fast/cornering, close your eyes for a moment on each one and let go of the bars. Sell the one that makes you smile the least. Works for me anyways....
(And if you want to be a highly scientific PITA, have Mrs OFG hand each to you and ride next to you on a quiet stretch while you are blindfolded and she can give you "left/right/straight" directions. That way you're not biased by the name on the bike. 1 will feel more lifeless than the others.)
I just let go of one of the rarest GT bikes I've ever come across, a handmade prototype that Gary Turner made himself. There were a million silly "collectible" reasons for keeping it. The young kid I sold it to was elated and I felt good about it afterwords... Sometimes you know if a bike isn't meant for you... (Of course if it pops up on ebay in 3 weeks I will kick myself)

If a bike doesn't thrill you and put a smile on your face when you ride it, it's kind of silly to keep it...