All of these cars are wonderful cars no doubt about it. I think it is a wrong decision to rely on what we say are, frankly speaking all of these cars are different and would suit different personalities and you'll be merely confused by the amount of different votes.
Nevertheless i will give you my opinion and i hope it helps:
If you're looking for reliability and expect the car to age and take the everyday beating without skipping a beat then Honda accord will be a wise choice. i dont know much about the drive of the Accord... I'm sure there are many Accord boys on pakwheels and they'll help you out here.
If you're looking for a comfortable cruiser with bit of luxury, expect a soft ride, and your driving style is sophisticated and not very sporty then Audi A4 will provide for your requirements.
I dont know much about hot hatches as i have not driven any or know anyone who owns one so i cant say about A3.
Now for my personal favorite from the list the BMW 320d. It is a car which is a perfect blend of sportiness and qualities of a comfort cruiser. It loves going fast and handles much beter than other cars you mentioned in your list. if you want a bit of a sporty recipe than BMW without a shadow of doubt will be best (note that i dunno about A3).
But keep in mind that BMWs are plagued with electronic problems and please do a thorough inspection of the car especially check all windows fuction properly and all the door locks function without a hitch. it is wise to keep about 1000 pounds extra if you are considering buying the bimmer to spend on the car and get everything checked up and sorted out.
Hope this helps...