12valves.... for when you want all the noise AND the vibration.
Honestly though...there's a time and a place for 12valves. They're easy to work on, lots of stuff available to add power and integration is very simple. They work well in many applications.
However, for a van...they are clackity clackity SOBs and given that the rear rocker box is like 6" from your knee, no matter what you do, that thing is gonna be "vocal" in the cab. Plus, the intake horn and fuel pump is in a not favorable spot relative to the brake booster/firewall. A 5.9L or 6.7L common rail fits much better...and they're much quieter.