For these words and others, are these forms interchangeable or are they regional? Or is one more poetic sounding than the other? Basically, when should one be used over the other?
For a word where both -es and -s are allowed genitive forms, -es is indeed considered more poetic, but could also be interpreted as outdated as stated by Maico Heere.
The Duden says that -es is preferred in constellations where the genetive is prefixed (e.g. des Tages Hitze) or within compounds with interfix-s (des Geschäftsfreundes).