My all-time favorite is the 6MM Remington! The .308 Win. is a close second.
I know that there is not much difference between the .243 Win. and the 6MM Rem. Both will kill any Whitetail on the planet, with ease! I just favor the 6MM Rem. Maybe it's because the 6MM was my first deer rifle caliber.

I grew up in Colorado and as my dad didn't hunt, I didn't start hunting until I was in college. Back then whitetail deer were scarce in Colorado, but I killed my first mule deer in 1965 hunting with my college roommate and using a .32 Win Special.

A couple of years later I got my first centerfire rifle, a .30-06 which was my main deer (and everything else) gun until about 1978 when I got a .257 Ackley. During that time, I also killed my best ever deer, a 30" non-typical muley in NW Colorado with a .45 caliber Kentucky percussion rifle that I built from a CVA kit, and I moved to Montana where I killed my first whitetail in 1975 with my .30-06.

Since I built my .257 Ackley just about all of the deer that I've killed were with that rifle, so I guess it would be my favorite deer rifle. I have however killed a few deer with my .22-250 and a few more with a .22 LR (which is legal in Montana).

I've killed most of my WT with 30-06 but in the pine woods my favorite is the 30-30.

For hunting the forested hills of Vermont I have used the 358 Winchester with the greatest results. since 1966.

My favorite rifle is the 99 Savage.

Wow, I have to many favorites. #1- 338 Federal, (Iam keeping the 358 win), #2- 308 win, #3- 257 robrt, #4- 30-06, #5- 30-30

.270 win.

.243win, .30-30 honorable mention.

As I live in Illinois it's been a long time since I went anywhere and used anything other than a bow or shotgun but have never been let down with the .30-06 in my Mauser 98.

only intimate with the 06

My long time (50+ years) No.1 go-to has been a 308 Win. I also very often use a 444 Marlin and sometimes a 6x5x55 SE.

MY first hunting gun was a 35 marlin I have all ways had a soft spot in my heart for that cartridge !!!