Which is better? Well, I have both, so I don't have to choose. However, the .280 is not loaded to it's full potential by the factories. This is IMHO, because Remington, in it's infinite lack of wisdom, decided that it should be used in pump and semiautomatic rifles.
Therefore, it must be loaded to a lower pressure.
They also made their pump and semiauto rifles in the .270 Winchester. If you check out the latest specs on the .270, you'll see it has been downloaded as well. Nothing that cannot be cured by judicious handloading in a good modern bolt action.
If I had to choose between the two, my preference would be the .280. However, being a bit more practical, ammo for the .270 is a lot more available. My local Walmarts don't carry .280, but they have lots of .270. Your choice.
Paul B.