Question Different features of Odyssey and Sienna?

I have read through a lot of these threads and they have been so helpful! We have narrowed our next minivan down to a used Honda Odyssey or a used Toyota Sienna.

We currently have a 2005 Dodge Grand Caravan, which is okay, but we haven't been overly impressed with it. It's had its share of problems and we're only to 51,000 miles on it. We have 3 children and we might, as in a very slim *might* try for #4 in a year or two. Currently our children are in 2 GNs and 1 TF. I would really like to keep these seats as they're all pretty much brand new.

I'm a little confused on the different features of the Odyssey and the Sienna. I drool over the 8 seater Sienna. We rented one on a Disney vacation and LOVED it. But I hear so many great things about the Odyssey, as in it seems that everyone who has one just adores them.

So, seating wise and other cool feature-wise, what are the differences? Top tether anchors for each? Stow-able seats? Gas mileage? Comfort? Lower anchors? Anything else that's a nice thing to have that I might not have thought of? Please keep in mind that we are talking about getting the least expensive model minivan we can find, aiming for around 30,000-50,000 miles on it. The budget is slim, but we think we can do it (we have a friend who is going to car markets for us). Thanks so much, everyone!

Just wanted to add that if we get the Odyssey, we'll be wanting one that's new enough that we might avoid the transmission issues of the older models (if that's even possible, not sure of the dates that got better?)

We don't have a quick and easy way to test drive these vans right now, so any advice to narrow the field further is appreciated. Sorry if this topic has been addressed before. I just don't want to have our friend bring a car home from us, only to find that it doesn't have many top tethers and the doors aren't automatic, etc.