One choir simply ends the piece and the other choir slows down (ritard) and changes the dynamics as well.
I don't think there is a right or wrong here. The ending of course would depend on the approach to the entire song. Sometimes ending a song suddenly has a great impact and catches the audience unaware.
Sometimes, slowing down too much makes your audience lose interest. They are just really happy you are done if you lengthen it too much. We have a song that has an ending phrase that really doesn't make sense to us. Instead of singing it we are treating it as a tacit (silence) and we think about it. We know we can't rewrite someone's music but we can think it really hard.
1. Consider your audience - Are they young and perhaps restless or are they able to absorb a more lengthy?
2. Does the ending honour the intention of the composer as you understand it?
3. Are all your endings the same? We were discussing an ending the other day and it was mentioned that some groups always end by "fading out". Be careful to change things up according to #1 and #2.
4. Do you enjoy singing the cadence? If you enjoy it then so will your audience. If it doesn't make sense then figure out another way. You don't need to change the arrangement but just the way you approach the music.
As we always say, the audience will remember the beginning and the ending so make them count positively.