I hear good things about the 6.5-284.....However, I am a 7mm nut, so I would lean to the .280 AI.
A .280 AI with some 168 Berger VLD's would be one nasty deer rig. And actually, my next full-on custom build will be a .280 AI for whitetails. But my next semi-custom will be rebarreling my A-Bolt II 7Mag with a new heavier contour barrel, so I can also get rid of my BOSS on the end that keeps unscrewing itself during days at the range, and throwing off my groups...Plus it's just a good excuse to put a custom barrel and true up the action.
7mmRemMag is also an excellent whitetail cartridge for up to 1K. And for up to 750 yards or so, the 7mm-08 is also a great low-recoil deer caliber, if you have an old short-action laying around. If you want whitetails beyond 1,000....The 7mmSTW will treat you right. I have all of the above in my arsenal at home...Or as I call them, my holy trinity (7mm-08, 7mm RemMag, 7mmSTW)....Get it? 777....Holy Trinity? Sorry, I have a weird sense of humor.
Just remember, there's a 7mm caliber for every purpose. And, you can kill anything in North America (probably the world) with a well-placed shot from a 7mm rifle. You don't always have to have a Howitzer, like some folks will tell you.