How can a person tell which one is best?

If the information about a plant calls for mulching with wood chips, does
it make a difference if one uses cypress, eucalyptus or something else?
How about the colored ones?

On a similar subject, do lava rocks and/or other (maybe heavier) rocks
do anything to hold moisture for the plants they surround or are they just
useful as weed barrier.?

thanks

Ana