I'd go for the Yaris.

It's got the most powerful engine, yet can rival the Jazz 1.3S in fuel economy. Larger than the Mirage, and more respectable too. In stock form, the Mirage looks as forgettable as any other minicar, despite just being recently launched. I find its styling to be more boring than the Yaris'.

Nevermind the toys of the Mirage, the overall fit and finish of the Yaris is still better for me. Plus, since parts are shared with the Vios, maintenance outside the CASA shouldn't be problematic. If you're the type to care about resale value, remember that the Yaris is a Toyota.