Depends a lot on which engine you have and the actual age of A3 you are looking it. Dispite all the negative comments so far, some of which are opinions, rather than observations from experiences having owned /driven one and not fact.....
My wife had an 11 plate 140 bhp 2.0TDi from work for quite a while, which was a torquey engine, with a good performance yet delivering excellent mpg. Felt very solid to drive and quite 'planted' on the road. Trim levels vary; this was a Sport model, which had a good middle of the range trim level, which felt well put together. Both sons have A3's of varying ages, a 6 plate and a 10 plate, probably drive them hard, but they are very reliable, and relatively cheap and easy to maintain.
As Focus' have been brought up, a couple of friends of mine have them, one a 04 plate 1.6 petrol, the other a 11 plate 1.4 (I think) diesel, yes good cars and pleasant to drive, cheap to run but don't feel quite as solid as the Audi and the build quality is not quite as good. Depends on how much you can afford of course, what you want the car for and personal preferences - as with any car.
No doubt the Focus lovers will now give me both barrels........