Whichever one shoots best...
I've got a 1/12 that loves 165-168 gr. Bullets. No makey no sense, but it shooots them a ton better than the 150-155 grainers.
It has a short tube on it, so I wish it liked the lighter bullets better so I could get the velocity up, but it is what it is...
actually, as i understand it, the 1-12" is ideal for 168 SMKs. my 700P prefers them as well and it's a 1-12.