Wait for the new Odyssey. Since you're asking this, i assume you've seen the next Odyssey. If not, here it is:
http://automobiles.honda.com/odyssey-concept/
Historically the Odyssey has always been better. Toyota is always playing catchup in the Minivan segment. The 2004 Sienna was made to compete with the 1999-2004 Odyssey, and they were very comparable for the year they were out together. Then in 2005 Honda came out with a redesigned Odyssey which romped all over the Sienna. The same thing is happening again. The new Sienna is pretty much even with the current Odyssey, but the next Odyssey is going to leap ahead again.