Old vs. New, in this case Old wins. I don't mind the new tabs but some people will, that is a questionable feature. Left/Right guys and girls was win.
One of the perks of the New though is the slight border on answers... sometimes following comments below an answer begs the eye to be careful not to run into the next question. I can see the previous horizontal style could adopt some of these features.
Also the top bar is pretty good. More or less. The margins are a little questionable... that is wasted space. :)