which filter type to use, mechanical, quartz or ceramic?

Hello I have a tube ssb balanced modulator and I am trying to figure out which type of ssb filter to use for 455khz.

mecanical, quartz or ceramic? Originally it used a mechanical one.

What are the differences related to unwanted frequency rejection anyway?

mechanical bandpass filter is best one.

I have read this somewhere else too, that mechanical filters have superior performance, hut I cannot understand why is that?

The mechanical resonators part of the filter can attain very high quality factor Q, which gives to mechanical filters excellent selectivity.
But the most important thing for a voice or CW communication system, the mechanical filters have good group delay response, making radios to sound different than others that use different type of filters.
A disadvantage of these filters is they have higher insertion loss than other types of filters.