I thought the Xbox startup was really cool when my brother got it for his birthday. Also liked the GameCube startup.

GameCube, PS1, PS2 and GBA!

GameCube is probably the best. The jingle is so iconic.
PS2 is pretty legendary because it feels otherworldly, and I would put the PS1 right around it.
GBA and DS are simple and great.
Xbox is cool like a science experiment.

1. Sega CD

2. Dreamcast

3. PS1

I'd also throw in the "Seeegaaaaaa" intro before classic Sonic games on Genesis, the "Sonic-a Team" intro that came later, and then lastly, the intro for all the Digital Pictures games that released on Sega CD . Not console intros, but cool nonetheless.

The Xbox One X Startup was cool. Definitely better than the Series X.

But:
1) PS2.
2) OG Xbox.
3) Dreamcast.

Ironically my chosen are all 6th gen consoles...

I'ma have to roll with the OG Xbox on this one.

PS2 startup still feels surreal even today. My favorite overall.

The Nintendo Wii is an odd one, but the transition from the health screen into channels felt very futuristic. If the channels are included then it's my favorite for Nintendo. Nintendo DS would probably be my favorite for handhelds.

The first xbox 360 startup was probably my favorite for the xbox brand. 

I don't enjoy the startups on current gen consoles (or even the most previous gen) very much. Modern consoles go right from startup into a cluttered menu that often includes a store, news, or live social features which for me breaks the immersion we got with old school consoles. 

The Gamecube and DS startups make me really nostalgic.

They do have a startup.

1. Dreamcast

2. Neo Geo

3. PS1

4. Japanese SEGA Saturn

5. Original Xbox