The Yaris HB cannot be had with sidebags. We chose the Corolla 'cause we have a wagon (Subaru) for carrying stuff and a compact sedan will do nicely. The Corolla has a very small fuel economy penalty over the Yaris, but is a much more substantial car in many ways. I also thought the price premium for the Corolla over the Yaris to be very small considering the difference in the cars. The Yaris sedan with "C" package (AT) is $20,360 with GST (Alberta) while the Corolla CE "C" package is $20,700. Only $400?
Now, the Yaris HB is more versatile, though the cargo space when using the backseat is very small.
One thing I do like about both Yaris and Corolla is the tried, tested, and true drivelines in both cars. Yes, the 1.8L for 09 in the Corolla is new, but has been installed in other markets previously. The four speed ATs in both cars are known bulletproof.
I think it comes down to preference when driving.