30.06, partly because it's what I have. I also have a .303 British I like but it was not a choice. Both shoot well to any common hunting distance and both are capable long range calibers. Plus they also perform well on large wild hogs.
Overkill, of course, but my favorite deer rifle is a Parker Hale surplus conversion German mauser in .308 Norma Magnum. I prefer it because it is so accurate and I have learned all of its range variations. I live in NY state and have shot a deer here at further than 40 yards only once. When I was stationed in Texas I did shoot a deer at 425 to 450 yards with the rifle. (I don't advocate doing that unless you have practiced with your rifle and understand the ballistics.) All but one deer was one shot. Most dropped in their tracks.
I have also used 30-30, 30-06, 35Rem, 12 ga, and 45-70.
I'm too old to stomp around the woods now, but I love my memories
I would have to say My Weatherby .300 Mag The area where I hunt is Sorrounded by long open fields.Averageing 300 yards long by 100 yards wide. I also use my Contender handgun Chambered in .356 Winchester.both have no problem getting the job done.
Whatever starts with 3. Right now I have a 30-06 that I am using and trying to get my 30-30 back from my brother. Many people prefer the .308 and it seems to have a little less recoil and the shorter throw is prefered by some. I like the 30-06 as it is about the most versital caliber made adequate for almost any medium to large game found in North America. I am lazy so I don't want to go chasiing a deer after I shoot it and the SCDNR studies say that the .3xxxxx caliber gives the best chance of that.
I checked .308 win although I really use 7.62x54R(RIMMED NOT "RUSSIAN") It's basically the same round, just hotter with a 3mm longer cartridge. Accurate, inexpensive at $12 for a box of 20 203gr SP and usually good out to 300m. I also use a 12 ga with 3/4oz HP slugs for shorter distance, I carry a few 3" shells for chance bear encounters which are becoming more frequent around here...
I shoot a 270 in a howa bolt action. The 270 shoots flat and has very little kick. have killed deer as far as 230 yards and as close as 5 feet using hornady balistic tip 130 grain bullets. there are many fine cartridges out there 30-06 270 308 and a host of magnums ,I say try as many as you can and pick what you like.Have fun hunting and be safe out there.