Team jacket - for sure!!
Jacket gives so much more structure, and is better at hiding the mid-section bits. I actually get a little depressed when the weather gets cold enough that a winter coat is req'd, since it's usually more comfortable to layer a cardigan rather than a jacket underneath. Or when it gets too hot for anything more than a very light, short-sleeve cardigan.
This is probably why Fall and Spring are my favorite fashion seasons - the ideal time to wear a cute blazer or jacket!!
Also, cardigans just don't last as long. They pill and loose their shape. Jackets are a much better investment.