I have an upcoming conference in Williamsburg, Va and I'll be arriving to BWI. Any suggestions on the best way to go from BWI to Williamsburg, train or rental car?

Best

While you might be able to get to Williamsburg by train I would suggest a car if you plan on going out (say for dinner) or doing any sightseeing.

I have driven from Washington DC to Williamsburg on quite a few occassions (live in DC, parents live in Williambsurg)

I think generally a rental car would be best but partially depends on what time you are arriving, what your preference for driving vs. train, how much time you have and what (if anything) you want to to while in Williamsburg.

Its a relatively slow / inneficient train ride because it goes to Richmond and goes very slow through the Richmond area. I have taken it from Washington DC on occassion. Its probably 4.5 - 5.0 hours from BWI to Williamsburg.

However, if you won't be leaving your hotel and really don't feel like driving and don't mind sitting on the train for a long time it could be a consideration.

Further, if you happened to be arriving on, for example, a Friday afternoon, the drive from BWI to Williamsburg would be rather painful.

I am sure your tickets are already bought, but flying into Richmond or Norfolk, VA (or even Dulles) would be much closer but i suspect more expensive which is probably why you are flying into BWI.

The fastest way, depending on your arrival time, would be to fly Southwest from BWI-ORF and rent a car. ORF is an hour or less drive from Williamsburg.

Otherwise, BWI is about 3 1/2 hours drive time from Williamsburg with no traffic...could be as much as 5+ hours though if the interstates are backed up. The Beltway and I-95 in Northern Virginia are pretty bad traffic bottlenecks, and even I-64 east of Richmond can be congested at times due to it only having two lanes in each direction.