What's the cheapest car insurance company you have found??

I just bought a new car–now comes full coverage & plates. It's a 2003 Mazda w/ 18,000 miles. Does the year or the mileage make insurance or plates higher? Do they request tickets for the last 3 or 5 years? You have to have full coverage when making payments right? I'm thinking Geico is the cheapest I've found so far?