I don't need a massive boot, but room for a car seat on the rear seats is most important with my daughter. I will find room for the rest of her stuff no matter what car i choose. I managed with a saxo, so i'm sure i'll figure it out!
I do like the Lexus IS, and as of yet have nothing to say against it. I will look further into it, same with the 159
I do like the look of the lancer, and it never occured to me to consider one. The figures of the octavia vRS are better (acceleration & fuel econ) so will discount that for now.
The budget of £13k is an absolute max, the car has to be seriously impressive for me to spend that much, i would be far happier spending £10k.