I think Beijing is more suitable to visit rather than to live in. Big cities like Beijing have fierce competition, and peope are awlays in a hurry. They have little time to enjoy the life, because they are forced to spending long time working hard to survive. It is reported that some middle-aged people break down under high pressure.
As the statistic shows, the divorce rate in Beijing is nearly 50%. How terrible!

And the weather, traffic, pollution......alas

However, traveling in Beijing is really a joy for ever, with lots of scenic spots worthy to be vistied. And the prices is cheaper compared to those in other cities.

I would say that Beijing is better to live in. Let me explain my reasons:

1) It is a big city: If you just visit here you will never really understand what Beijing is really like. Of course there is pollution and way too many people but it also has a lot of hidden gems you will never know unless you spend time to explore the non-touristy parts of the city.

2) Beijing has a lot of cultural events. If you just visit you will not experience them all.

3) As a lover of history I like that there is bits of history everywhere you go in Beijing. Again if you just visit it is hard to truly experience this.

I don't really agree with QTracyQ. I feel that for a big city like Beijing, the rythm is pretty slow and enjoyable and people take the time to go out and visit. I dislike Shanghai's rythm though, too fast and definitely westernized in the wrong way... people care about appearances! 
As for whether it's better to live or visit, i think there is no right answer... In french, we say 'the neighbour's garden always has a greener grass than ours' and i feel it applies here. If you're living in BJ, you'll complain about this and that. On the contrary, if you visit, everything may seem great because you need not to worry about those daily stupid little things...
Try it, and judge it for yourself...

Considering this is the capital of China and there are a lot to see and do it would probably be better to live in for the short while. As far as health it is probably not that good to stay for a long long time but for living a short while would be nicer than just visiting for 1 or 2 weeks. In that period of time you can't possibly see everything and do everything in Beijing. You would have to live here for a short while to actually do everything and experience everything that the city has to offer. Visit the great wall and all the best tourist spots. I like what Beijng has to offer as far as that but the pollution is the big problem that I have but I've gotten use to it. I also dislike all the spitting on the ground that I see and not just the pavement but places like shopping malls and public transportation.

it would probably be better to live in for the short while.