This question seems to come up monthly...
In general, I'd suggest model years 2007+. Many of the problems with the earlier vans were fixed at this point (power door cables come to mind). Plus, the 2007+ vans came standard with stability control and traction control, which was only available on upper trim levels in previous years. Finally, 2007 was the first year of the 3.5 liter engine, which replaced the 3.3 liter engine. The 3.3 was known to sludge if the oil wasn't changed at regular intervals. The 3.3 is also a timing belt engine, which needs to be replaced every 100k miles at $700.
In general, I'd suggest model years 2007+. Many of the problems with the earlier vans were fixed at this point (power door cables come to mind). Plus, the 2007+ vans came standard with stability control and traction control, which was only available on upper trim levels in previous years. Finally, 2007 was the first year of the 3.5 liter engine, which replaced the 3.3 liter engine. The 3.3 was known to sludge if the oil wasn't changed at regular intervals. The 3.3 is also a timing belt engine, which needs to be replaced every 100k miles at $700.