The type of jacket you'll possibly need depends on the time of year you walk your Camino. If you walk in the Summer, you might not require a jacket at all (but you should probably carry something lightweight that will keep you dry if it rains). In the spring or fall, it might still be cold in the elevations, and there's always the possibility of rain. Of course, winter provides it's own issues with cold, snow, rain, and sleet.
When I walked it was Spring into early summer. We only had one day of rain over about 7 weeks. While we were walking north on the Via de La Plata, a friend of some pilgrims I was traveling with who was on the France Way experienced 30 straight days of rain. One truly doesn't know what's going to happen.
I carried a raincoat that tucked into it's own pocket. Convenient and light from a packing standpoint, but boy was it uncomfortable to wear. The Spaniards I met were wearing coats made out of Gortex. Lightweight and the fabric kept them very dry.
In preparation for life (I spend some time in the elements even when I'm not on a Camino), I purchased a Mammut rain jacket. It's Gortex, so it keeps me very dry, and it has an adjustable hood that allows me to keep the thing up and away from my eyes so I can see while walking and hiking. While not cheap, I found it well worth the investment.