Well, sitemaps are, of course, very good, google can locate your pages easier, however the sitemaps dont help your SERP's rankings or positions or pagerank or whatever. I have seen good results by using google sitemap's.
I bought the Stand Alone XML-Sitemaps and I found that it is nearly the same as the phpsitemapNG, but the developer put more effort on XML-Sitemaps, more features and updates are being introduced.
XML-Sitemaps will break the sitemap file into several files if 50,000 links limit reached. It uses sitemap index to link the other sitemap files.