You will get a million opinions, but the reason is that there is no real answer to your question. There is no "best" caliber out there. But I will give you some guidelines:

If you are never going to hunt anything but deer, a 270 can't be beat.

If you think you might want to hunt bigger game such as elk in the future, the 30-06 is a good choice.

Both choices are flat shooting, several bullet sizes to chose from, modest recoil, and ammunition is readily available most places

There will be people on both sides of the spectrum that will tell you that you can get by with a smaller cartridge and they have killed 50 deer with a pea shooter and those on the other side that tell you that they only use a 50 caliber 1000 yard sniper gun. However the calibers I gave you (used as a minimum) will never let you down.