The branches of my family tree are bending low under the weight of
John William people! As far as I know, they all went by
Jack.
I like
John too, and I'd personally never use
Jack as a stand-alone name, but that's just me.
John Keith Robin would be surprising.
John Gregory.
John Richard. Not that they're colourful exactly, but the current scarcity of
John people would make anything work.
I read once about a
John who started school in England - secondary school presumably - and after a few days came home in a towering rage and demanded of his parents "What did you give me a weird name like
John for? Why couldn't I have a normal name like
Jason or
Justin?"