A Boeing 757 plane operated by Delta Airlines.AaronP/Bauer-Griffin/Getty ImagesDelta Air Lines topped The Points Guy's 2024 best US airlines list for the sixth consecutive year.TPG's rankings assess four broad categories: reliability, experience, cost and reach, and loyalty.Interestingly, ultra-low-cost carrier Allegiant Air scored beat out Delta in overall reliability.The busy summer travel season is here, and airlines are working hard to keep their planes and people moving without much headache to the customer.However, some are better than others.Travel website The Points Guy published its annual list of the 10 best airlines in the US on Wednesday.