Sgt_Kickaxe - 12:05 am on Nov 24, 2012 (gmt 0) [edited by: Sgt_Kickaxe at 12:09 am (utc) on Nov 24, 2012]
From a pure SEO standpoint "pagename" would be best, it's all the information you need to share though none of the examples would likely be considered bad by any major search engine.
From a useability point of view I prefer "pagename.html" simply because, if I choose to, I can create a static copy of my php pages and upload them to the server to completely get rid of the CMS or php script. There is nothing faster than full static pages(no database, no processing etc) and those work well with the old .html extension (unless you like mucking around with htaccess redirects and such).
I use both, it depends on the site.
[edited by: Sgt_Kickaxe at 12:09 am (utc) on Nov 24, 2012]