Mozilla/5.0 (Linux; U; Android 2.3.4; zh-cn; HTC Sensation XE with Beats Audio Z715e Build/GRJ22)Maxthon AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1
Compare this to the user agent of the default Playbook browser:
Mozilla/5.0 (PlayBook; U; RIM Tablet OS 2.1.0; en-US) AppleWebKit/536.2+ (KHTML, like Gecko) Version/7.2.1.0 Safari/536.2+

Hmmm, just noticed some weirdness with attempting to apply some labels to this post, but I think it was because I was zoomed in.
So what makes a good web browser? Besides web pages rendering as intended by the page author, if you're going to do anything where you have to type some characters (this may include typing a URL or search term) and if you don't have a hardware keyboard, you should have good text editing capability. That is, auto spelling correction and cursor repositioning, and for productivity: copy-and-paste and text selection features.
[Updated August 2, 2013]