There's no such thing as an "impression" when it comes to reliability, just statistics.
Since anyone on an internet forum would be making up results out of thin air, or based on claims like consumer reports, etc, it's not worth having a discussion.
If you asked a BMW quality engineer, I'm going to take a guess and say yes, the N55 is more reliable. Why? Because they sat there for 4 years and analyzed all the failures on the N54 and redesigned it to improve the quality (go Six Sigma!).
Current: '15 M235i Vert
Previous: '13 335i, '08 TL-S, '00 Corvette