i'm using google Authenticator and have no plans to change it.
why?  I do not care about design of app, all I need is the raw functionality
also it is important that google is working on every exchange
and I have a little more trust to it, then let's see this open source app - yes, it is open source, that is good for any who is ok with the code, but if you know nothing about programming, then for you it is no use.
anyone who have good skill in programming may add some bad code to it, compile and you can download this bad app.. surely this bad code will be detected and wiped out, but it will take some time, while you will be on risk..
that is why I think for me there is no cause to change Google Authenticator for something else.
it is working, right? so let it be working further