We pay the minimum - we have an offset account and keep all our money in there, it reduces the interest and we have easy access to it if needed. It's much better than paying extra on repayments.
For our investment property, we only pay the interest, so the principle amount doesn't reduce. The rent from the property covers the interest payments so we rarely need to put money into it these days.
It all depends on your strategy - we prefer to buy smart and leverage the increase in value (either growth in the value of the area/land or by renovating). DH doesn't believe in paying off mortgages!