Clearly the first one (ignoring for now that scrolling on Safari was jerky when I tried). The old one is fluid which is just a bad idea for long texts. Much more than about 100 characters per line reduce readability, using all the space on a 1920 pixel wide monitor is just a bad idea.
The new version could maybe have about one third wider lines but the seventy or so characters are a good number for texts on the web. The new version is beautifully typeset and has about the right line length.
Using all the available horizontal space on the web for text is nearly always wrong.