I have four sites that were ranking ok with goog for most of my keywords but I didn't like the program so I switched to one that uses php ext. After a year my rankings are still junk. Bottom line it, which extensions does goog prefer? This is rediculous.
Google has absolutely no preference for any particular extension. However, changing extensions after you've already established your site puts all your pages on brand new URLs. Unless do the 301 redirects from the old version to the new, they're all starting over from scratch with Google.