I prefer to use actual chip count for normal play - early levels and even later in the tournament when I have a big stack. In these situations, the only thing I care about is "who do I have covered" or "who has me covered". There's no difference in my play whether I have 50 big blinds, 75 or 100 or more. I don't like to see the big blind numbers, I can easily tell when opponents are getting short (which should change how they play but I don't care much about that if I have them covered).
However, when I get short-stacked, then I much prefer to use Big Blinds because it becomes critical to do one thing at 30 bigs, another thing at 20 bigs, still another at 15 bigs and when we get to 10 bigs or less there's really only "shove or fold" at that point. So I generally switch over when I detect I'm beginning to get short because now every blind I have becomes critical to my strategy, just a few big blinds can dramatically change how I approach the hand.
So I use both and this method works perfectly for me. When I play on a site such as BetOnline which doesn't have the option to switch, I have to do the math in my head and that makes it a bit more difficult... plus, BetOnline does not offer very large time banks, at least at my micro level... doing more math leaves me less time to think about my play, so its a bit frustrating... and they also offer no hand histories either, for reviewing our play afterwards... so get your act together BetOnline, get with the times, get with the program!!