With the Olympus spend a tenner more and get the 14-42. It's newer, sharper, shows less chromatic aberration, it's lighter and prettier. As I said, Bristol Cameras have the camera with the 14-42 for £335
HERE.
They also have the twin lens kit (14-42 and 40-150) for £450
HERE.
As I said above there is nothing wrong with the 17.5-45 per se, its just old and obsolete. Why not get the better one if you can?
I didn't know the Pentax ran on AAs. You can use rechargeables in it so you wouldn't have to buy loads of batteries. Some people would consider it an advantage because if all goes wrong and all your batteries are flat at least you can buy AAs in a shop!