desmol, as you are probably more exposed to warm weather, I would definitely propose summer. I was in Iceland in August/early September and things really seemed to be closing down after beginning of September. I have done the entire ring road (by rental car & tent) and it was a great trip. I can definitely see you getting stuck on the ring road in winter. Most of it is a 2 lane street, sometime there might be gravel. I suppose in winter there might be areas with little to no traffic. We have seen graves of hikers who underestimated forces of nature in Iceland. Keep this in mind. As far as Auroras are concerned, I would recommend a transatlantic flight in Jan/Feb.