IME:
Sienna has a roomier and more comfortable cabin for ALL passengers, not just the driver. Handling is a breeze and super smoothe. The starting models tend to run a BIT pricier than the honda, but basically the same.
Oddysey has a tighter drive on the road for the driver. The control you have when driving IMO is superior to Sienna's. Its not sooo spacious like its counterpart.
Both have an excellent lifespan and will keep up better than Kia or Chrystler.