I use safari almost exclusively since firefox was bogging my macpro down. I have been playing with opera because it has some really sweet features but it is buggy and seems about 2 versions away from prime time.
The new top sites page has a few minor tweeks but what is really awesome is the inclusion of the history tab. This brings the history flow feature that was buried in version 4. I actually think I may use it in this version. The browser may be hard review at this point until some real extensions get built for it and not ugly SIMBL hacks or application wide system processes. It would be nice to have a real xmarks of adblocker plugin.
The coolest addition is the reader button that pulls an article's information off of a webpage and displays it as if it was a pdf or word document without all the distractions on the site. I have played with that the most and it is very very slick.
In some ways this application is a disappointment as it supposed to represent the cutting edge in the web. It falls short in a few areas:
No ability to sync web-history or bookmarks across browsers (without using tethered sync or apples outrageously expensive mobileme service). This is something that opera and firefox are both exploring and an area apple could really leapfrog people on.
No plugins available yet (not apple's fault).
Not a ton of html5 sites to play on (also not apple's fault).