With a 30-30, ALWAYS shoot for the heart-lung area. A 30-30 does not have the impact power necessary to kill a deer instantly if the high shoulder shot does not hit the spine. And the spine is a small target. I always take heat for saying this, but the neck shot is a TERRIBLE practice, as is any shot intended to hit the spine. The spine is a tiny target (about the size of a broomstick). I know VERY few hunters who can make that shot consistently under the influence of adrenaline.
And now que all the neck-shooters...
I hate to count the number of deer I've helped unsuccessfully track that were neck shot. It's a bunch.