Cello for me

I like the cello a lot.

Rhodes

Tuba.

Gotta have that sweet bass. Maybe some Flight if the Tuba Bee or Tuba Polka by Canadian Brass. Chef's kiss.

Love me a clarinet. Also a muted trumpet is pretty pleasing. I think though the most across the board genre neutral pleasing instrument timbre is the piano. It does it all.

Bari sax

Handpan, just so mellow sounding.

Church organ. The larger, the better.

Oboe.

Cello and steel tongue drum

Organ (powerful deep tones, not the high whistles)

My favorites are eastern instruments that have a meditative quality, like the Indian tanpura.

Also whatever instrument this man is playing.

But I think above all I'm a fan of the American steel guitar. That wailing sound evokes nostalgia and melancholy like nothing else.

Very bassy bamboo flutes

Get me a good Rhodes and I'm in bliss. A good horn section can squeeze a beautiful chord melody. And a bagpipe is what I send to my enemies.

Do synth pads count?

Clarinet, Bass Clarinet, Oboe, and Bassoon.

Violin. Cello. Basically any stringed instrument played by rubbing a bow across the strings, actually.

Im a jethro tull fan and im not sure if that is why im partial to the flute or the other way round.

Listen to a lot of renaissance lute music. Very mellow.

Firstly, this assumes that "timbre" is a fancy word for "sound characteristics". I would definitely have troubled defining it.

Piano.

For me no contest.

Zurna. Definitely Zurna.

slide whistle

Marimba

Definitely the cello; especially when played like Zoe Keating.

French horn and glockenspiel.

I don't know the name of the instrument but its the one playing the main melody in the credits of The Legend Of Korra. Brings tears to my eyes with how expressive it is.

Theremin is beautiful too when played well.