Chrome (and thus Blink) supports the HTML5 standards better than Safari.
Just look at http://html5test.com/results/desktop.html
Chrome 26: 468/500
Safari 6.0.3: 378/500
Maxthon (the winning browser 476/500) is likely to switch to Blink as well - it's based on Chromium.
This doesn't say anything about correct support. Chrome supports more HTML5 functions, but it doesn't say they are all correctly implemented. Apple is holding off with a lot of the implementations because they're either not stable or the specification isn't clear on how to handle things exactly. This only confirms that Google is using code after very limited testing. Apple waits a whole lot longer.
General opinion
For web developers this can be good and bad news. In the last 2 years or so Google has been making changes for their internal WebKit builds that are part of Chrome. Breaking some websites that work good in other WebKit based browsers. As Google left the WebKit house it may make it's own changes to their engine that make it look like the new IE 6. It's also easier for Google to optimize the browser for their own services and downgrade the performance on other companies' services.
On the other hand WebKit got a little bloated in recent years and that not only slowed development down quite a bit, it also let to many problems with memory consumption. A lot of the bloat comes from the hands of Google. Most of the core work is being done by Apple and I hope they can keep a focus on those things. The companies using a WebKit port will have to look out more for themselves now or join Blink.
Apple also pulled away quite a few key-engineers from the project to work on other things. Apple has been using WebKit as a recruiter tool for new developers since the project went open source, but so far that didn't bring the project the force it had when it was first released as part of Safari 1.0. I don't think Apple will be able to fill the void left by the Google engineers soon as Apple is on an engineer shortage, partially because an office space shortage.