alasta: As others have said the Lancer is really aging - the current generation was launched here in 2007 and doesn't appear to have had a major update since. I hired one in Australia a couple of years ago and thought that it felt cheap - the switchgear almost seemed as if it was going to fall apart in my hands - but these vehicles are very affordable to buy new so they're obviously designed to meet the price point.
The Mazda 3 isn't entirely to my tastes because of a couple of minor issues that probably wouldn't bother most people. However it is widely regarded in the motoring press as being top of its class and consumers seem to consider it to be highly desirable.
The i30 improved markedly with the launch of the current generation back around 2013. It's a very good vehicle but some might consider it a bit dull compared with the Mazda.
There are issues with any car though. Would be interested in the issues you don't like. One of the things I don't like is istop, which stops the engine when you aren't moving, and starts it again when you need to move. You can't turn it off permanently either, although there are work arounds, such as tilting the wheel when you stop. The heads up display is also not the greatest, and it is a pain to adjust it each time a different driver drives the car. Although these things aren't just restricted to the 3.