I'm only selling on the Yaris, as we've decided to move from 2 cars to 1, since we are now both commuting on public transport.
The Yaris has been excellent, I actually bought it after owning a Fiesta - in the 2 years of owning the fiesta it was in the garage about 10 time (and it was only 18 months old when bought).
The Yaris on the other hand gets it annual check up and the only 'problem' in 4 years of ownership has been a puncture. When I bought it the only criteria I had was that it works: key goes in, car starts! And its never let me down on that very basic requirement.
You will pay slightly more for a Yaris than an equivalant sized car (micra, fiesta, etc), but if you keep it for a few years you find that it saves you on maintenance costs.
The only other piece of advise I would give is that you get a good level of reliability buying Japanese.
Mell61
PS: Take out membership to an auto rescue service, be it AA or RAC, you may never need them but it a nice security.