FMA keeps true to the source material iirc halfway through? Then it completely derails and gets really bad imo. FMAB follows the true ending and is what is actually popular and beloved due to having such a great ending. Some people recommend watching like the first 30 eps of FMA then starting on like the 7th episode of FMAB since they’re the same or smth? Just start with el 1 of FMAB and you’ll be fine