The wider the tire the more traction. But regarding what will is ideal for the car and what will fit, ideally you'll want to stick as close to your OEM sizes. 215's is a good choice if you want to size up.
Regarding all-seasons, they'll perform better in wet and snow conditions but won't give you as much grip/performance as summer tires. Also, all-seasons generally have a longer tread life compared to summer tires because of the rubber compound. So you can gauge what will work for you with the weather you experience and your driving style. I hope this helps.