Not so far ahead of rock-bottom Spirit, Frontier Airlines sits ahead by just 2 point at 68 points. This is still pretty low, and it is very possible you would have a turbulent flight (in more than one way) if you flew with them. The Similar to Spirit, it has actually improved slightly from the previous year, increasing by 3% in Customer Satisfaction. The airline is also ultra low-cost but offers more destinations than Spirit, with 116 possibilities. You should know however that this airline was subject to a class-action lawsuit after it refused to refund passengers who had their flights cancelled due to the Covid-19 Pandemic. Best to avoid.
At least with Allegiant Air we finally get a score above 70! Allegiant Air sits uncomfortably on a Customer Satisfaction score of 72, which is still someway off the top. I say uncomfortably, because even though Spirit and Frontier are below, they had a positive increase from the previous year. Allegiant however, has only decreased by 3%/. Allegiant has had its issues in the past, such as filing for bankruptcy in 2001 and has been monitored closely by the FAA for too many emergency landings and aborted takeoffs.