GameCube is charming and Dreamcast is etherealy beautiful, but nothing beats pressing that Xbox power button and feeling like you just started up a nuclear powered machine from the future.
The OG PlayStation is my childhood. The Sony logo goes almost as hard as the THX deep note. And then waiting with anxiety for the disc read to succeed on a scratched up disc, anticipating the sweet release of the PlayStation logo and sound.
Despite never owning one until just a year or two ago, Dreamcast is definitely my favorite. Had a PSx but never played much, yet it's still my 2nd favorite.
GameCube's was fun because you could make it wiggle by messing with the controls. Gameboy had something similar where if you played an OG Gameboy game on GBC, you could mess with the controls to select the colour scheme
The first time my brothers and I booted the original xbox was a major and magical moment in my childhood. So techy and sci fi it felt like starting up some sort of reactor or spaceship.
I don't really care that much for whatever the startup is but the one that is most seared in my mind is the simple saga one. the sound really more than the look but the look always accompanies the sound. mostly I think due to shadowrun.