Welcome Alan,
You really need to have a good drive of both. In view of your apparent driving habits the 1.4 petrol will most likely be the most appropriate. The two benefits of the the Diesel are the fuel economy and the torque.
We don't get the 1.4 Petrol in Australia, but being a much smaller motor than what we get,obviously the difference between the economy of the two will be much less. This reduces one advantage of the diesel.
The torque factor which makes the Diesel feel so much stronger and more powerful (particularly on hilly winding roads) can be quite addictive. It gives the i30 a bit more "character" in my opinion.
In the UK, all Diesel i30s come with a DPF (Diesel particulate filter) which we don't yet require in Australia. Some Hyundais have them over here but not the i30.
This slightly reduces the diesel's economy and isn't suited to a situation involving mostly short trips. It requires fairly regular sustained motorway journeys to do a regeneration "burn"
But I still recommend you drive them both to experience why there is a difference in price.