I considered the Odyssey and Sienna to replace my 00 Chrysler T&C LTD. I had a better selection of Sienna's, and their reliability is reported to be much better than the Honda.
The selection of used Sienna vans was much better than the Odyssey vans. I was able to bargain one dealer against the other dealer due to the number of similar Sienna's for sale. Not so with the Odyssey.
The Sienna has a telescoping and tilting steering wheel but the Odyssey does not telescope. I found it easier to reach a comfortable driving position in the Sienna.
The Sienna is a bit less harsh on bumps then the Odyssey. The Odyssey seemed to be slightly more agile.