TheOptimizationIdiot - 8:17 am on Mar 18, 2013 (gmt 0)
I'd just go with the documentation [sitemaps.org...] and use the options as they're defined and intended since I can't remember any search engine ever saying xml sitemaps were used for ranking purposes rather than helping with discovery especially on sites that are difficult to crawl and possibly "which URL to show" when there's a question, even though (incorrectly) some "SEOs" may have.
Oh, just answered the question and saw some of the previous posts earlier, but didn't see JimBeetle's until now, so "what JimBeetle said".
I will add: It's really sad to me to see search engines get the blame for what some "SEOs" (used loosely) incorrectly state. Search engines (their reps / documentation) haven't ever to my knowledge stated xml sitemaps could or would be used for ranking purposes, the only place I've heard that is from "SEOs" who don't know wtf they're talking about.