Seeing that colorbond/gal roofing has been thrown into the discussion, I think it is fair to say each has their advantages and drawbacks:
Terracotta tiles are baked clay and has the potential to last roughly forever. They are lighter than concrete but, as Rolf points out, not as strong (or perhaps a better term is "more brittle"). Available glazed or unglazed, although I think I read that unglazed terracotta tiles can be almost as heavy as concrete because they absorb some amount of water.
Concrete tiles are cheaper, have a limited lifetime (although still pretty good), and are heavier.
Colorbond is lightweight, cost-effective (but I don't think "cheap") but it is noisy in heavy downpours and provides little ventilation to the roof space. I don't think you can reasonably expect the longevity of colorbond to match either terracotta or concrete tiles. Certain substances cannot be used in conjunction with colobond, for they cause the colorbond to corrode. My memory can't recall what they are, but I have read somewhere that even rainwater runoff from an incompatible surface could be problematic. Don't know how leaves and their tannins might affect colorbond, but it could be a consideration.
In a fire-prone area colorbond might be a better choice because it is a sealed roof (except under the roof edge) thereby reducing the chance of embers entering the roof.
Some people might consider terracotta roof tiles a more "upmarket" product (in cost, they are) over concrete tiles if you choose to resell your property later.
Fortunately your house previously had concrete tiles (the heaviest) so it is now capable of holding any style of roof.
I don't think you will be disappointed with either choice, so long as you choose a good brand etc. Aesthetics will also play a consideration - there is usually a wider range of profiles available in concrete tiles - I'm not sure how the color ranges compare).