One of the major advantages of diesel vs gas is torque and fuel efficiency. Pero kung sedan po and all around city driving lang, baka po negated itong advantages ng diesel vs gas (aside from the fact that mas mahal initially ang diesel variant). You are better off getting a Jazz, City, Vios in no particular order.
AFAIK Hyundai accent and Ford focus pa lang yata mga diesel variants dito. Also consider your annual mileage. If it will be less than 10,000Km/year, gas na lang po. 15,000 and above, in the long run, diesel will suit you more.
well, if you need some help in the pricing...you can read this little nugget. It'll give you a little more information when negotiating with the dealer.