Hard to advise really without knowing your budget, are you buying new or used?
Agree with the above poster that the Focus is a good car, 1.6 petrol seems especially well-loved, the mk 1 is cheap and plentiful now and spares are also cheap.
The Golf is expensive for what it is and VW's are not as reliable as people think they are (dealers don't always give the best service either)
The Yaris is a good wee car (cheap on the second hand market now and reliable) Don't forget thought that despite the trick rear seat it is still a small car.
Don't discount the Skoda Fabia or even the Nissan Almeira. The Almeira has no image but is cheap, roomy reliable and surprisingly nice to drive.
The French cars (Megane/ Pug 307) are cheap, safe (esp the Megane) and nice to drive but very patchy on reliability.
The folks in the back room on this forum are always willing to pass on knowledgable advice too:
http://www.honestjohn.co.uk/forum/index.htm