There isn't a right answer to that...
You need to handle the cameras to see which you like the most.
Personally I don't like the Sony a230, it's plasticy and feels cheap.
The Olympus is a better camera but the 17.5-45 is an odd lens. It is only available through Currys/Dixons companies. You'd normally get the 14-42 which is better.
Edit: The 17.5-45 was the kit lens sold with the E-500. It's not a bad lens per se but it's old now. When Olympus introduced the E-410 and E-510 they also introduced the 14-42 and the 40-150 to go with them. There are a few back to back reviews of the 17.5-45 and 14-42 and the 14-42 is generally better. Links to the Olympus website with info on each lens are here for the 17.5-45 and here for the 14-42
The Pentax doesn't do as well as the Olympus in most reviews (but the differences are minimal). You are looking at a twin lens kit with the Pentax which could be a bonus.
It really depends on what you want to shoot. The Olympus will has an advantage in the telephoto lengths because of it's 2x FOV multiplier rather than the 1.6x of the Pentax and Sony.
I can't tell you which is "best" but if it were my money I would avoid the Sony (unless you can find a used a200 rather than the a230) and I would be torn between the Pentax kit (which is better simply because it has the extra lens) and the Olympus (which I personally think is the better camera).
And I'd be thinking this all the time while I was buying the Olympus with it's proper kit lens (the 14-42) from
Bristol Cameras for £335