Well
if you have the mics and you don't know which one to keep, how should anyone else know?
I'm not trying to be a smartass (it just comes naturally), but you have them. You know what they sound like on what you've tried them on. Only you can know which one you like better.
In terms of being all-around useful, conventional wisdom would say keep the SP, as it would be more of a jack-of-all-trades for instruments. But, if you like the way the 67 sounds on your voice, and you want an occasional alternative to the AT, then there you go.