First, lets take a look at the Ford vans.
The quick and dirty to the Ford vans is as follows: Rear differentials are great, nearly all transmissions offered are good, motors are good runners but several have a common issue (which is a huge pain but fixable), suspension is an older/stiffer but tougher design.
Now, onto the details ...
Read Ends - Ford rear ends found in these vans will be the 8.8" and 9". Both are very stout, have tons of aftermarket support (helpful if you want to change gearing), and will generally be problem free. People often forget that the rear differentials need services. Swap to synthetic gear oil and replace the gasket. These units should hold up for the life of your van no problem.
Transmissions - What was used depends on your vehicles years and motor choice. Suffice it to say that with regular maintenance they will all serve you well. That said, the Ford offerings here are known for being fine right up until they aren't. They will also be the most expensive to repair and replace of the Big 3. Upgraded components are available and suggested for long trouble free life. Synthetic fluid is a MUST. The AOD transmissions are known for great highway MPGs but poor city numbers due to gearing.
Suspension - Ford utilized an older front suspension design right into the 2000s called a "Twin I Beam". This setup is extremely durable but has two key issues. First, it will offer the most truck like ride of the Big 3 vans. This means that it will be a bit harsher and likely have more body roll. Second, this older design does a much poorer job at optimizing suspension geometry when compressed. In other words, all the nice angles your suspension uses become goofed the more load you apply. This has resulted in many complaints of uneven tire wear a premature suspension issues. However, this problem has an easy fix. Get your van aligned when it is at full weight. An alignment when empty followed by laden driving is the issue. Having your alignment set for the same weight and weight distribution you will be driving under negates this issue almost completely. Now you have a properly set suspension which is by far the strongest of the Big 3.
Motors - This section has to be split into two categories. Motors in vans 97 onward are different and have a specific problem. Here is the breakdown.
4.9L I6 (300ci "Truck Six") - 96 and earlier - This motor will be harder to find in the vans vs trucks but if you find one ... buy it. This is easily one of the top 10 gasoline motors ever produced. Nearly unkillable, amazing power and fuel economy, gear driven timing means no timing belt or chain to worry about.
4.9 V8 (commonly called the 5.0 or 302ci) - 96 and earlier - This is the same 302 we find in Mustangs and Explorers as well as a dozen other vehicles. Cheap and easy to work on, ok fuel economy, lots of aftermarket support, but generally considered a little underpowered for the vans as the low end torque is lacking compared to other options.
5.8 V8 (Windsor 351ci) - 96 and earlier - Gobs of torque and pretty darn reliable. Fuel injected models deliver reasonable fuel economy. Valve cover gaskets often develop leaks.
7.5L v8 (Lima 460ci) - 96 and earlier - One of the last gas motors produced that can tow a house. They will run forever but pretty much max our at 12mpg and commonly return 8-10mpg.
Now, onto the 97 and later Ford Modular (Triton) motors which have some pretty serious issues ...
For whatever reason, Ford decided to produce these motors with VERY few threads in the head for the spark plugs. Blowing a plug right out of the head is not unheard of. Furthermore, Ford used a 2 piece spark plug design that is well known for breaking off in the head when you try to remove them, disabling the vehicle. It is so common that a special tool is made for removing the bottom section after it breaks off. Replace these plugs ONLY with aftermarket 1 piece plugs. Also, 97-01 motors have a common failure of the plastic intake manifolds where they crack and dump coolant (thankfully, most vehicles on the road today have already had the manifold replaced by Ford).
4.2L v6 (Essex) - This is the smallest and lightest duty motor available. Not a bad motor but too underpowered for a big van loaded with stuff. Fuel economy will suffer greatly in a laden vandweller setup.
4.6L v8 (Triton) - This is the same motor found in everything from later Mustangs to Lincoln TownCars. A good compromise between power and fuel efficiency so long as your setup isn't super heavy.
5.4L v8 (Triton) - Most common motor to find in the full size vans but WILL suffer from the above mentioned issues. Good power and fuel economy for its size.
6.8L v10 (Triton) - This is the big monster gas offering. If you're not towing just avoid it. Fuel economy is abysmal and it has the same problems noted before.
Other - Expect to replace fuel pumps and starters often (Especially on older models). Power steering setups tend to make a lot of noise but they last if you avoid cranking the wheel all the way until it stops and turning the wheel when sitting still. Ancillary equipment (AC, alternators, etc) typically hold up well.
In summary ... Older is better because you avoid the Triton motors, while newer motors have issues they can be addressed (though it may be labor intensive), transmissions hold up well with regular interval synthetic fluid changes. If issues are addressed ahead of time and they are maintained properly they can easily be the longest living vans of the Big 3. I rank it #2 on the list.
