is break fly actually BETTER ??

Break fly is better paired with def shred debuffer such as pela and SW, I choose Pela instead because of AoE def shred. FF got innate 40% def ignore through her traces, adding +18% def ignore with new relics so its 58% already, add Pela's ultimate for +42% def shred for a total of 100% def ignore. Therefore Pela is best using Before Tutorial S5 instead of Pearl S5 LC to avoid def shred overflow and allows Pela for SP neutral 2 turn ult rotation.
Answering the title :
Both outputs ridiculous damage, can't go wrong with any of these two. Just build the way u want to play it or adjust with the RnG relics on your account. I personally like crit fly more than break fly, it opens up an option for me to bring crit amplifier support in case of sustainless run.
Stage: MOC 12
Team Comp: E2S1 firefly, E0S1 Ruan Mei, E6 HMC, E6 Pela
*Crit Fly = Crit + Break Hybrid (Crit + Break Effect to achieve 40% ignore def)
*Break Fly = Full break effect, no crit
*This is V1 Kit, and is subject to change before releases.
*I didn't mentioned E1 FF kit in v1 even though it's basically another def ignore because right now her E1 is bugged, I saw other CC tested it and see no difference or miniscule dmg difference.

[@uggasabian8114]

interesting, it's 0 cycle team for FF.