I was recently faced with the same question, I had £14k to spend and needed a five door, reasonably quick (and nimble) car in return.
It was between the MK5 Golf GTi or the Focus ST, and here is what I found;
The Golf seems to be appreciated as the better built car, slightly better handling, was more composed (Boring in my eyes), and had a slightly more grown up image.
But, the Focus was more fun, faster, and didn't have tartan seats. (Plus I could get a top spec, low mileage example for my money!) But the thing that really sold the Focus to me was the fact that if I went for a Golf, I'd have been buying a car that was a year or two older with twice the mileage, for the same money.