I vote for the 1.9 TDI for four reasons:

1) It has a wonderful torque curve that is ideally suited to the Vanagon

2) If it fits cleanly under the engine lid

3) If doesn't require an adapter plate (unless you have an automatic)

4) I sell the conversion kits and do installation (okay, this one is a
little self serving)

Cheers,

Jeff
www.vanagonparts.com