It really, really, really depends on (in my opinion) two things:
1) The kind of van your spouse (or whomever will primarily be using it) gravitates towards, including the features that may be important to you.
2) Your willingness to DIY repairs.
Point one is nearly face-punch worthy and sort of goes against the forum, but I can tell you right now my wife would have been far less pleased with a Grand Caravan than with our Odyssey.
If you're looking at older, less expensive models - your baseline should be an early '00s Odyssey or Sienna. Avoid older Chrysler/Dodge vans.
If you're looking at something that's 5-10 years old, the Sienna and Odyssey are still going to be the best two options.
You don't really need anything newer than ~5 years old, the newest Odyssey and Pacifica are ones to avoid (in my opinion). The Sienna and T&C/Caravan haven't been updated meaningfully in nearly a decade.
Most of the vans between 2007 and 2014 have similar features and similar drivetrains (power doors, liftgate, etc.) but all differ on smaller options and repairability. Each also has its own issues that you need to be aware of and look out for.
The best van you can find is one that's clean, has average or below average miles for its age, and has an accessible repair history. The Odyssey, Sienna, and to some extent the Quest all hold their value fairly well, so you're not going to be able to find something way below average price without a bit of luck.
Last year, upon learning #3 was on the way, we purchased a '14 Odyssey with slightly below average miles for about $1500 under the average asking price because it had been for sale at a Chevy dealer's used car lot and in this region, your average car buyer going to a Chevy lot is looking for a truck or SUV, not a Honda van.
All this being said, because these are the MMM forums, have you seriously considered alternatives to a van? In our case, we could justify the need for the extra trunk space and our kids don't like the Diono Radian style carseats. But, if we didn't need the space or the kids didn't mind the seats, we would likely have stuck with our Mazda CX-5 or upgraded to something a hair larger. Do you really need a van, or could you get away with a small SUV, station wagon, or other similar vehicle??