If you are going to have only one rifle, I would go with a 30-06. Great availabilty of ammo in different weight bullets and bullet types. If you choose to hunt larger game in the future you have it covered.

Sounds like you may be a one rifle man so you need to make one good choice. Nothing wrong with that. I would have to suggest sticking with the standard chamberings for versatility and availability. The .270 Win. will take any deer walking with no problem. The .30-06 will be even more versatile. I am afraid the Short Magnum may be just a craze. The .300 WSM is probably here to stay, but in the long run a person may find the old tried and true chamberings more friendly.

I'm gonna have to agree with James B.

You can search for something better than a .270, but you won't find it. The .270 WSM should be an excellent choice.

If I had to use just one rifle it would be chambered in a 7 Rem mag

You've already recieved a deluge of useful information, so I'll keep this brief. I use a .243, but I know that it is a bit light for the bigger deer in the world. .270 and 30-06 are great rounds. 7mm-08 is great too. The great thing about .270 is that, wherever you might find yourself, you can buy .270 ammo. The nice thing about 30-06 has to be the versitility of it. I don't personally see any need for a magnum. If you ever forsee yourself hunting elk, nilgai, or caribou, go with the 30-06. Otherwise, you should like the .270 fine.