8mm Mauser Euro spec or .308.
I would probably have to vote .270 as the ideal North American deer cartridge, but I like guns with a military connection, and .270 is a purely commercial round and only comes in a limited variety of guns (that is, mostly commercial hunting rifles). I'm not someone who only shoots 5 times a year---3 times to sight in and 2 times at deer. I like to shoot.........A LOT.
And there is no arguing the effectiveness of the ol' 30-30 when used within its proper range. Not prestigious enough or macho enough for some I suppose, but it works...
1944 Mauser byf K98 8mm, K31 7.5 x 55 Swiss, Rem M700 Classic 8mm, 1920s Colt New Service .45 LC, Browning Hi-Power and HK P7 in 9mm, SAIGA .308 22", SKS 7.62x39mm, S&W 686 Plus 6" and Taurus 617 2" in .357 Mag, Ruger MkIII Target 5.5" BB .22LR, Mossberg 500 & Marlin 120 in 12 GA, etc.