Main transit hubs in Europe usually are those that have the cheapest fares. From my own private knowledge, I’ve uncovered that London, Amsterdam, Frankfurt and Milan are usually cheaper to fly into than other more compact cities. Flights is usually filtered by various components for example airline, airport and price; https://meshbookmarks.com/story19648289/5-tips-about-how-to-find-cheap-flights-to-europe-from-the-us-you-can-use-today