United Airlines and Spirit Airlines both have significant negative feedback from users, but the specific complaints vary. United Airlines is criticized for its poor website usability and extremely negative experiences, while Spirit Airlines is often referred to as the 'Greyhound bus of the sky,' implying a very low-cost, no-frills experience. The 'worst' airline may depend on what specific issues are most bothersome to you, such as website usability or overall service quality.

Spirit Airlines is often referred to as the 'Greyhound bus of the sky.' It is a low-cost carrier that offers budget-friendly flights across the United States and to various international destinations.

As of now, there are no user-generated pros and cons for flying with Spirit Airlines. Generally, the pros of flying with Spirit Airlines include low ticket prices and various flight options. The cons often mentioned are additional fees for luggage and in-flight amenities, and sometimes less legroom and comfort compared to other airlines.

Spirit Airlines flies to a wide range of destinations across the United States, Latin America, and the Caribbean. Specific routes can be checked on their official website.

Spirit Airlines charges additional fees for checked baggage, carry-on bags, and even for selecting seats. It is recommended to review their baggage policy on their official website before booking.

Spirit Airlines does not offer a built-in in-flight entertainment system on their planes. Passengers are encouraged to bring their own devices and entertainment for the duration of the flight.

United Airlines is a major American airline headquartered in Chicago, Illinois. It operates a comprehensive domestic and international route network, making it one of the largest airlines in the world. United is a founding member of the Star Alliance, the world's largest airline alliance.

Currently, there are no user-generated pros or cons available for United Airlines. However, general feedback about airlines can vary greatly and may include factors such as the quality of customer service, in-flight amenities, punctuality, and ease of booking.

You can book a flight on United Airlines through their official website, www.united.com. The website allows you to search for flights, compare prices, and complete your booking. You can also book flights via their mobile app or by calling their customer service.

United Airlines offers a variety of services including in-flight entertainment, Wi-Fi, meal options, and different classes of seating such as Economy, Economy Plus, Business, and First Class. They also provide a frequent flyer program called MileagePlus, which allows passengers to earn miles and redeem them for various rewards.