I suspect flying up front on any of the majors is fine. Economy experience is driven by a race to the bottom price-wise, but if you want cheap travel, it’s readily available. If you want comfortable travel, that’s also on offer.
I flew Frontier the first time this Spring - was helping ferry an open cockpit biplane from Colorado to Illinois - and it was a stupid cheap one way fair. I really can't think of a single perk Frontier did not try and up charge a fee for. Boarding, luggage, carry on, seat assignment... I'm sure there were others. Funny enough, the guy I was ferrying with also picked the cheapest seats in the plane, so we ended up next to each other on the flight out. I was fully prepared too wear the kevlar helmet on the flight rather than pay the $60 carry on fee.
It's probably important to be specific when I say "quality." By that I'm referring to ease of purchase, fair baggage prices, web/app UX, on/off-flight customer service including pilot communication with passengers, and even landings (as a pilot, I am absolutely judging beyond "did we get to the ground safely or not"). Price and seating are secondary for me, although I certainly understand why they are list-toppers for others.