Not to start up any acrimonious exchanges (honestly) but regarding the original question - it seems a bit of a 'no brainer' if one is looking for some a bit 'different' the .280 is clearly the choice.
Regarding any 'theoretical' differences, well I don't see how .007" bullet diameter can possibly make much of a difference in anything. However, if being slightly 'bigger' makes the .280 clearly 'better' in any absolute sense, then clearly necking down is a bad idea, so the .25-06 must just be worthless. Further, it must have been a bad idea to neck down the .30-06 at all, so both the .270 and .280 are worthless. Finally, it must clearly be advantageous to neck up the .30-06, making the .35 Whelan the ultimate logic development of the .30-06 cartridge case, for all purposes. Since none of that is true, and necking up or down has it's own trade offs and compromises, then the .270 Win must be ever so slightly better than the .280 Rem in some regards and the .280 Rem must be ever so slightly better than the .270 Win in other regards.
That being said, in practice they each also have distinct differences. The .270 Win is clearly more popular overall, which has advantages in terms of availability of various rifles chambered in it as well as factory ammunition. For reloaders, there is a wide variety of 7mm bullets available, of various designs. For those that like to 'tinker', the .280 Rem has great appeal as a cartridge that didn't quite live up to its great potential. For those that just want to find a rifle of their choice chambered in a round of that class, preferably at a good price, and likewise easily find factory ammo for it, similarly at a good price, then the .270 Win is the way to go.
