Personally I have found Jet Blue to be highly variable. When I've flown them cross country (SFO-JFK) it was great- plane was very nice, awesome snacks (and beverages) that you can help yourself to, great infotainment system etc. But when I flew them on a shorter trip (OAK to LGB) the experience was very different. Plane was more cramped and grungy, snack/beverage service was traditional and didn't have any particularly special options. I can't remember if there weren't any seat back screens or if they were so old as to be unusable but either way was not impressive.
None of that would make me not fly JetBlue again as it wasn't really that different from plenty of other airlines out there (I fly a lot for work on a variety of different carriers. I had an awful American plane/experience two weeks ago on my return leg, for example, but had a really a nice one on my outbound leg) but the difference between the two experiences was striking. JetBlue went, for me, from a bit above the rest for domestic airlines to pretty much the same as everyone else. I think that's one mark in Southwest's favor- their's is a pretty consistent experience. There are ways to ensure you are "head of the line" and get to be first on board and effectively pick your seats but even without those I've never had an issue getting a satisfactory seat on SWA both flying solo or with the family.