I just completed my CB test today. Overall, if you are comfortable using computers and typing on keyboards, then I would highly recommend taking CB over PB. They also provide sheets, pencil, pen, eraser and a sharpener (most of which you won't need) for rough work. I really liked the CB. I have previously taken the PB for Academic last year, which was a pain right from registration (long waits) to the actual marking on the test paper.
Having said that, the listening test was a little tricky. I am not sure if CB had anything to do with it, though. Last year, I scored really well in academic (L, R, W, S: 9,9,7,8) on PB. So, this time I went in overconfident, but listening test in general this time was much more challenging, so a bit worried about getting low scores.
One thing that annoyed me was that the computer screens, although nice and large, were covered over with filters that restrict viewing angles. So basically someone trying to take a peek from the side cannot see what's on your screen (which is good). But this filter would make the periphery of the screen blurry, whenever I was looking at the center. I was basically looking at the monitor like a lizard with constant side to eye movement to 'unblock' this effect. Maybe that was just my monitor.
You can also adjust text size, color, background color etc. before every test for your eye comfort. And did I mention the small waiting time for results?