Aygo's are fine but at that age check underneath for rust, especially rear sill near wheel arch. Front bumper will need a respray - it's a common issue on that ago, the paint goes on the front bumpers as the lacquer peels off. Aygo's and their Pug/Citroen versions leak around the boot, and that one would suggest the seal on the rear lights needs replacing. Common leak points are rear lights, boot rubber seal, rear high stop light and the two bump stops for the boot hatch. All easy to fix, but it's not something you can leave.
The Yaris is a better drive, again you need to check underneath cars of this age as it depends if the previous owner(s) ever washed off the underside - road salt left on causes loads of issues. A Yaris isn't all that big - it's wider than the Fiat, possibly a smidge longer.
