Jetstar are great, my wife and I boarded a Jetstar plane in Cairns to fly to Sydney a while back. We had seats 5A and B from memory but the seats on the plane went from 4 to 6 with no row 5. The steward made us wait near the toilets until the rest of the passengers boarded then they would see whether they could find seats for us. They eventually found a couple of seats and apologized for our inconvenience, they then said it happens all the time on that plane because of the missing row. From Sydney we had another Jetstar flight to Adelaide, went to check in and were told our flight had been cancelled due to insufficient seats being sold. They told us to sit down and they would try to find us a couple of seats on another flight which they eventually did on a Virgin flight.
Worst airline though would go to Etihad, flew with them from Abu Dhabi to Sydney, 14 hours in the smallest airline seats I have ever sat in. I am 180cm (5"11") and slim yet my knees were in the back of the seat in front and my shoulders were wider than the seat back. Service was non existent, they closed the curtains and dimmed the lights for the entire flight and the stewards all disappeared to the first class section. Apparently that is usual when there are spare seats in first class.