• [pack] creates a compound list from input atoms of a preset type (symbol float or pointer).
• [list] creates (appends) a compound list from two input lists (these could be a floats or symbols because [list] will a convert these input elements to lists automatically).
• [list] itself is not really an object but a wrapper for [list append], the list family is made up of ![list append], [list prepend], [list split], [list trim] and [list length]

So, for two input floats there is no matter which to use?

If you are using floats it is best practice to use [pack], as it has type recognition and will output errors if a foreign type tries to get calculated. And of course [pack] can handle more than two inputs..