With out a doubt it would be my .243. I have hunted with .06's, .270's, 7mags and everything in between and I love the .243 the best. With velocity's hovering at 2400 fps at 300 yds, low recoil , low noise levels, super flat trajectory's and tendancy's to drive tacks I believe it is the ultimate deer caliber.
You have to shoot one for yourself, the confidence levels you achieve are like no other, place the cross hairs where you want, shoot and watch the deer fall through your scope (no recoil) its that easy.
The little 100 gr. bullet does tremendous damage to deer, its like the perfect speed for a given bullet weight. It does more damage than biger calibers. Check out my post on the 2 deer I killed this year with it. Click the link below.
http://forum.hunting.net/asppg/tm.asp?m=459864&mpage=1&key=