I feel like people often look back at Heavensward with rose-tinted glasses.

It's still my second favorite expansion for many of the reasons people have already mentioned and the elf camping trip arc to get answers from Hraesvelgr was among one of the high points for the entire game. But then there was other stuff people tend to leave out of their nostalgic memories like having to go back to deal with Ul'dah junk, the waaaaaay too long moogle quests that interrupted the main story, the multiple versions of HW Diadem, BRD and MCH being forced to sit still as casters, MCH having a really un-fun RNG rotation and DPS much more reliant on ping, certain Alexander raids were so frustrating that it permanently damaged friendships, Wiping City of Mhach feeling like purgatory upon release since there were so many mechanics that a single person could mess up that could wipe the alliance.

Shadowbringers is looked at fondly IMO for a bunch of reasons. It tightened up the story really well so we weren't split between distinct arcs that broke the flow of the plot. The "cute mascot break" that HW, SB, and EW did here felt more natural and integrated into the plot by having them connected to Urianger and a Lightwarden while the "cute mascots" themselves still presented an element danger. The Scions are finally all present at the same time again with equal screentime and they each received character growth and attention from the writers. The WoL went from a silent hanger-on to more important NPCs who were actually doing the important things to suddenly being the main protagonist who is driving the plot.

Shadowbringers felt like its own game in itself while Heavensward just felt like just another (good) expansion.

My brother who has played way more Final Fantasy games than I have but hates MMOs even picked up FFXIV just to play ARR through Shadowbringers and then quit after he finished it but said the Shadowbringers piece is his top 5 of FF stories.