As a very first image, I would image all partitions - for the case that the HDD breaks. From then on you only image C and (if available) the data partition.
When you have a system malfunction, you restore C only. When you have a virus, you restore C and the data partition. When your HDD breaks, you define new partitions on the new HDD. They must be equal or greater in size compared to the original partitions. Into those you restore the images. If you have a 100MB active partition, you mark that "active". Else you mark C as active.