For romance 7x57 (karamojo Bells favorite) I own 3. Also 257 Roberts. I have one, Rem. Mod.722, belonged to my father in law.
I have, and greatly like, my two 6.5 swedes.
Lastly my Ruger No1 in 270.
If I had to pick just one caliber to shoot, and to hunt with in the lower 48 I'd pick the 6.5x55. A choice based on emotion, since the 7x57 and 270 maybe more versital for larger game.