I have read all the posts in this informative thread. It has stirred debate and provided some interesting comments. However, I feel the OP's question is somewhat off base. I own and shoot both the 270 and the 7mm RM. In between the two, I also have a 7x57 and a 30-06. Like many of you, I have guns smaller than a 270 and larger than the 7mm mag. To those that say the 270 is a tweener, you are correct. Every single caliber rifle is between two others.
So what's my point? Would anyone ask a pro golfer a question about whether he thinks his 5 iron is better than his 7 iron? Each club serves a different purpose, so there is no better or worse. Just different. There is a bit of overlap too. And under certain circumstances, you can make do with what you have. I saw a golf instructional video one time, where a club pro played three holes, a par 3, par 4 and par 5 with just a 7 iron and a putter. He put the ball on the green in regulation on the par 3 and 1 over regulation on the par 4 and par 5. He ended up playing the 3 holes in one or two over par and emphasized the importance of hitting the ball reasonably well and keeping it in the fairway (think shot placement).
Does this question make any sense? What's better, a Ford F-150 or a Ford F-350? Both are Fords so sort of the same, but one more in the car category with light hauling and the other for more serious towing/hauling/work. Different vehicles for different jobs and yes they have some overlap. Doesn't make one better or worse, just different. Of course if you are a Chevy guy, both Fords are junk.