I have .308, .243 and have recently added a .223 also. I think your choice needs to be led by the following questions..
What will you be shooting with it on your own ground?
I have fox, munti, roe and occasional fallow and any rifle I have is more than capable of dropping any of them on the spot with correct bullet choice and shot placement. At certain times of the year the land is literally covered with livestock and many foxes are shot in amongst the sheep/lambs – probably wouldn’t choose the .308 for that, even the .243 with 55gn ballistic tips has some pass throughs, that’s why the .223 has been added. However the .308 has taken a few foxes and certainly does the trick, with 125gn b tips it shoots 1” high at 100 and 1” low at 200. With 55gn ballistic tips the .243 is like a death laser out to 300m, but the weapon of choice at the moment is the little .223.
What invites will you be getting, and what would your host prefer you to use?
I get a few invites a year and for some the .243 would probably not be as welcome as the .308, especially for the larger deer that are sometimes encountered. If I am going specifically to shoot deer I take the .308 every time and if I was taking a complete novice I would definitely put the .308 in their hand to get their first one on the ground – quicker the better. Saying that, there are people out there who prefer the smaller calibers and the chance to give their dog some work!