My brother has the 1.4 100bhp petrol and my mate has the 1.9 100bhp tdi so I'll give you my opinion, the petrol sounds pretty good, fuel economy isn't bad and is pretty nippy. The diesel feels a lot faster, though obviously doesn't sound as good.
If they were both the same price then it'd be a no brainer, get the diesel, if you're intending on modifying i.e remapping, or you do high miles, again get the diesel, if not I would be inclined to get the petrol, I don't know if I could justify the extra cost buying the diesel.