Hi, of course I'm biased toward W&M, but here are some things to consider:
Cost of living -- D.C. will be more expensive, but D.C. is a good city. Williamsburg is a very easy and beautiful place to live. It will be a very different experience here than in China.
Personal attention -- GW is a good school and has a good reputation. However, W&M is a smaller and more intimate place. You will take all your classes with JDs and be on a LLM curve.
There is not much difference in the rankings -- #20 v. #24.
If you want to email me in person, please do so and I'm happy to discuss. jsstevenson@wm.edu
Take care and both schools are very good, so don't stress about your decision! You can't make a wrong one with GW and W&M!