Is 30 minute chess best to improve?

Do you smoke that or take it orally?

I prefer 30 minutes Rapid on chess.com though on Lichess I prefer to play 10/3. Longer time controls cut down on blunders by allowing more analysis of the position. I admire people who play well in Blitz, but that is not me.

Play whatever time limit you're comfortable with. I play 60-minutes games because I'm in my late '70s and just don't process information as rapidly as I once did. After losing several games at 30 minutes, I switched to 60 and have won most of my games since. I would suggest beginners use longer time limits until they get some grasp on opening principles. Even if I were younger I doubt I'd play many blitz games. Unless highly rated people are involved, the chess just gets too sloppy.

no. 90+30 is the only way to improve properly.

bullet is the best

Probably because you have more time to think and have control of the game

Yes