Twig default filter or Null coalescing operator?
So things like the null coalescing operator make it easier to chain things, so if you have a number things to fall back on, it's much neater to write:

{% set woof = bark ?? howl ?? growl ?? null %}


...then it is to try to chain that all together with | default filters.

Something that may also make your life easier is the Empty Coalesce plugin, so you can write:

{% set woof = bark ??? howl ??? growl ??? null %}


What's the difference? The null coalescing operator only checks for null, so if bark = "" then it'll choose that, which often isn't what you want for strings.

There's a writeup of all of this in Handling Errors Gracefully in Craft CMS article.

Now, what is going to be more performant? Unless you're in a massive inner loop (which we should avoid in a templating language anyway), I doubt it'll matter. PHP code is transpiled to a bytecode that often gets cached, it should be fine.

But in theory, ?? and ??? are probably marginally faster.