I’m fortunate to have flown many airlines in the states, including most of these budget airlines. Discounting the fiasco that is Allegiant Airlines, you get basically the same thing at ALL airlines, from Delta down to Spirit. The difference is how they deliver the service.
With your budget airlines, you pay for what you get. This means if you’re traveling somewhere for a weekend and can pack just a carry on (or better yet fit your belongings into a small backpack), you come out on the cheap end of things. Also, if you’re not someone who eats snacks on planes, you again come out cheaper as you dont’ have that added expense. Where you start to run up the bill is if you check a bag, picked a preferred seat and/or buy snacks on board, your overall cost is nearly equal to that of a bigger carrier. If this is the case, go with the mainline carrier over the budget. The big difference between the two is the customer service. Bigger air carriers, such as Delta and American, for example, have the infrastructure in place to handle customer dissatisfaction and the occasional surprise hiccup.
For example, I flew from LAS-MSY on Spirit last year. When I got to the ticket counter, I was 3 minutes past the 45-minute check in time for travelers with checked bags. I travel often and with bigger carriers, this has not been an issue. They have been willing to work with me and find a solution. Spirits solution was to decalre that I missed the flight (even though It was no where near leaving) and I had to take the flight offered later in the day. This came with an additional $100 dollar fee for each person. At a bigger airline, this would have been handled in a better way (I know because I’ve had it happen.)
I really like budget airlines, depending on the flight. I think they’re great for people that need to be more budget conscious when booking a flight. They do, however, tend to not be very customer friendly, and end up costing the customer more money in the long run vs. their competition.
My opinion: Spend the extra money upfront and avoid budget airlines when possible. Your wallet and sanity will thank you for it.