Why not use both? Both are legendary calibers for different situations.

30-30: perfect out to 100 yards in heavy brush, thickets, etc.
30-06: perfect out to 300 yards in open fields, brush, thickets, high country out west, etc.

I have a Marlin 30AS 30-30 with plain open sights and I love it for the thick woods and ridges here in Virginia. One of these days, I'd like to compliment it with a nice .270 or 30-06.