It's a difficult question. There are some I love, like the 7mm Rem Mag and .300 Wby Mag, but there have been many evolutions in cartridge design which has done things like eliminate the belt. I love the boring old .30-06 as well, especially when stoked with modern bullets and powders it really comes alive.
It's probably not in existence yet, what I'd really love to see is a 7mm or .30-cal on the Weatherby RPM case. Smaller bolt face than the PRC cases, more powder capacity than the .280 AI. You could probably match .300 win mag factory loads and still fit it on a .480 bolt face in a 3.340" COAL. 180 grain bullets at 2950 is the business.
If I had to absolutely pick one, I would lean towards the .30-06 myself. Maybe a .280 AI, ultra close second today (might flip that around by tomorrow).