Ennies Lobby is better
1. Iirc it is the first time Straw Hats had serious internal conflict (Usopp vs Luffy and Robin leaving the crew).
Comparison to Soul Society, Gotei 13 had internal conflict too like Gin vs Hitsugaya, Kenpachi vs Komamura + Tosen, Yamamoto vs Ukitake + Kyoraku and Aizen pulling the string from shadow. Yet by the time both arc came, I think readers feel way closer with the Straw Hats already than Gotei 13 Captains (Soul Society is only second arc while OP already had long adventure before Ennies Lobby) so Straw Hats' conflict felt more personal.
2. Most of main characters got a big match up in Ennies Lobby. Luffy revealed gears, Zoro got Asura, Chopper revealed Monster Point etc.
Only Usopp didn't get big fight but he got Sogeking moment (way better than God Usopp imo) and burning the flag.
In comparison to Soul Society, it kinda felt more like WCI than Ennies Lobby: only the MC Ichigo got big fights one after another (Ikkaku, Renji, Kenpachi, Byakuya) while the others got sidelined, especially Chad, which at that point was still portrayed as 1 of Ichigo's Monster Trio team along with Ishida.
Straw Hats got better focus than Ichigo's original 5 team in SS arc. Monster Point was really cool back then.
3. The ending for Ennies Lobby is far more rewarding.
Usopp came back, Robin came back, Franky joined, and they got a new ship. As a stand alone arc, that ending feels more satisfying imo than Soul Society arc, which revealing Aizen betrayal and only became a set up for the future arcs.