Which would you prefer, a full page refresh that will refetch a large portion of the page that you're already looking at or an ajax call that will return far less bytes than a full page refresh would have and then replacing only the parts of the page that needs changing?

Also if its truly isomorphic, everything would still work as usual if javascript is off.

I want the page I'm looking at to be mostly the content I'm interested in, so when I follow a link to get more content most of the page should be updated. Under those conditions, a full page refresh is preferable because it works nicely with the browser history, bookmarking, "Email this Link" feature, and anything else I might want to do with the page of content.

I should have prefaced my original question with "all other things being equal...".

I believe you can have browser history, bookmarking, email this link any thing else you might want to do with the page in a single page application and also get the benefit of not doing a full page refresh.

Single page application are reletively new and kinks are being worked out but if I could have my cake and eat it too, I wouldn't stand in the way of those trying to make that a reality.

How about loading the whole page on each click, and front caching the parts of the page (nav etc.) that are repeated on each page. This would have really good performance, and be simpler than building a single page app when one isn't really required.