Are you in one of the markets slated to launch with 4g? If so, waiting might be worth it. If not, a 3g phone now should last you until 4g comes.
A few things to consider:
1: If you sign a 1 year contract for the droid x, you can upgrade as early May 15th of next year (meaning that not only will more places have 4g, but there will be a slew of devices)
2: Verizon's gone on record saying that they're looking at tiered pricing for 4g, and they seemed to hint at a total rework of plans (you being able to buy data in bulk and use it on multiple devices) While this could be a boon if you are in 4g areas off the bat, it could mean paying more initially until 4g hits your area.