I can't say anything about the .270 Winchester that hasn't already been written unless I lie. Introduced in 1925, the .270 is a necked-down .30-06 that holds .277 diameter bullets. The darling of the late Jack O'Connor, legions of fans are willing to go to fisticuffs to protect the good name of the .270. Don't believe me? Walk into the Seven Devils Saloon in Riggins, Idaho, and tell the patrons that the .270 isn't worth much as a big game rifle. At the very least no one will buy you a beer.
Unlike the .270 Winchester, the .280 Remington has been struggling almost since its inception in 1957. It also utilizes the .30-06 as a parent case, and as it's necked down to .284, its bullet is exactly .007 inch larger than the .270. But the latter enjoyed a 32-year head start, and the .280 suffered from some bad fortune—one being a name change from .280 to 7mm Express then back to .280, the other being the introduction of the instantly popular 7mm Remington Magnum.
The .280 has spent most of its life pinched between the popular .270 and the 7mm Remington Magnum, and it competes against several other commercial 7mms as well: the blazing fast 7mm STW and 7mm Remington Ultra Mag and the low-recoiling 7mm-08 chief among them.
With all this going against it you'd think the .280 would have shuffled into obscurity, but this hasn't happened. Why? Well, let's remember the .280 is very closely related to the .270, and the .270 formula works well.
Anything that you can do with a 130-grain .270 can be done with a 140-grain .280. The longer, heavier bullets available for the .280 give it a higher ballistic coefficient, and when loaded with 175-grain bullets the cartridge offers a sectional density of .310, meaning it will penetrate in heavy game — although this can be hampered by the .280's velocity.
From a ballistics standpoint this gives the .280 a slight advantage over the .270. Which one you ultimately choose depends on whether you prefer the tried-and-true .270 or you root for the underdog .280.