I wear both,but my jumpers are very lightweight.I think that with the tropical days usually becoming rather warm by afternoon,cardigans seem to be more practical for me at the moment.I am wearing a lovely soft angora one at the moment!!
I wear either/or, usually with a long sleeved t-shirt, then I can peel off layers as necessary. I find going in and out of shopping centres the temperature varies so much you are either sweating bullets or chilled to the marrow, so it is good to have a couple of layers you can peel off or put on!
I used to wear a long sleeve shirt, with a jumper,
jeans or slacks in winter, but now as I only wear dresses summer & winter, in Sydney, during winter, I wear a cardigan (& jacket if itís cold enough,) & a cardigan with either jacket/coat in Melbourne, during winter.