According to the most recent Air Travel Consumer Reports and J.D. Power satisfaction studies leading into 2026, Frontier Airlines and Spirit Airlines consistently receive the highest volume of complaints relative to their passenger numbers. These "Ultra Low-Cost Carriers" (ULCCs) often draw ire for their "a la carte" pricing models, where fees for bags and seat assignments can frustrate travelers who aren't prepared for the extra costs. However, among the "Big Three" legacy carriers, American Airlines often sees a higher complaint rate regarding flight cancellations and baggage handling compared to Delta or United. In 2025, Southwest also faced a surge in complaints related to its transition away from "open seating" to assigned seats, which split its loyal fanbase. While Delta typically ranks highest in "on-time performance," it is not immune to complaints regarding its high fare prices. For travelers, the peer-to-peer takeaway is that reliability often correlates with price: you are statistically less likely to file a complaint on Alaska or Delta than on the budget carriers.