I concur with Walksondirt... if your 09 Yaris is in good condition and meets your needs, it is by far the most environmentally friendly and economical choice when you figure in both the capital and operating expenses.
If your needs have changed or if you've driven the Yaris into the ground, you should consider a Prius V (!=Prius 5, poor naming) which, IMO, is a better car than the Prius.
Be cautious though, both the Prius and Prius V are very loud cars at highway speeds. You may want to take an extended test drive to see if you can tolerate it. My wife and I were going to buy a Prius V (we test drove it a lot, were happy with it except for the highway noise) but decided at the last minute that with our long trips we really couldn't stand it. (We went with a Camry, BTW).