I would personaly prefer an older gun. The challenge, and therefore some of the fun, comes in finding the one that fits your personal demands.  With a new one, it will be made to measure.  The difference in $$$ however can be great.  A high condition game gun from the 1930's might cost as much as $50,000.  More if a 16, 20, or a 28; still half the price of new. Earlier 12 bores in fine condition can sell for less than $30,000; and guns that need a bit of TLC for under 20.  Another option is to buy a gun with good barrels and action and have it stocked to fit you.  
All the best, Mal