A year ago we went through the very same dilemia. I was convinced I wanted a Honda Oddosey. We went to the dealer (in KC) to check them out. We looked at the 8 passenger vans because we have a large family. I was surprised that the "8th" seat that was in the middle was so small it couldn't hold a car seat, let alone one of my children. We also had been driving a 1999 Ford Windstar. For space, we felt the Honda Oddessey wasn't really much bigger. It did have better understorage in the back. We were looking at the 2008 models. They were about $28,000 new, off the lot. They were making a deal because all the 2009 models had arrived.
We decided to go check out the Sienna's the next day before making any decision, since we had heard that they were equally as good. Well, we found a van and we LOVE it! We found a used 2008 model that had 11,000 miles on it. It had been a rental. It is much bigger in my opinion than the Honda. It's wider and has more leg room for both seats in the back. Our oldest child is 14. He's 6 ft tall and weighs 240 lbs. He fits comfortably in the back of our Sienna. This would not have been the case with the Honda. Also, we paid $22,000 for the van. We got the 100,000 mile bumper to bumper warrenty only because of all the troubles that the Windstar gave us. (We put 2 transmissions in it).
We did have a battery go out in the Sienna, but it was replaced at no cost. They said it was just a bad battery which can happen with any vehicle. I LOVE my van!! I expect to keep it for a very long time. I'm pleased with the customer service with Toyoyta company also.
If you want to spend less money and get a bigger van - then go with the Sienna!!!