I personally like the old Twitter because it's quick and easy for me to use (since I'm familiar with it). I really have no interest in going through a learning curve to get use to the new one. With that said, I mostly use Hootsuite web app to use Twitter so I'm really only on Twitter.com when I'm trying to clean up my account or edit my profile, etc.
New twitter is attractive with added some additional options like about the overview of the particular twitter user while clicking on the tweet of the user which appears on the right side bar. And in old twitter we are familiar with the options as we are using it from long time. I will prefer to use new twitter to get more overview with additional options.
Old twitter is definitely my choice because of its simplicity. I think twitter should give users and option to choose between old and new twitter.
I'm familiar with old one but new is attractive and have more features than old... With the passage of time we will be familiar with new as well.... then no one will like the older one.... Latest is always better as I think...
I only use the old one and filled out their survey saying why I didn't change. I specifically like the old design, the way you could actually display a background with information, and their navigation.
I like the new Twitter, now that I am use to it. I did prefer the old Twitter for awhile though, but the new Twitter grew on me.