Based on your 3, I'd pick Charleston - hands down. But @ that time of year, I'm much more likely to visit New Orleans or Key West.

I love Seattle (I live here) and it is a very walkable city, but I would NOT suggest it for a 4-day vacation in JANUARY!

Charleston is a wonderful, very walkable city. However, it can get pretty cold in late January. We were in New Orleans last year for Thanksgiving and needed to to buy sweatshirts to layer with the jackets we brought. For a four day trip in January, I would choose Key West.

bachslunch, you are correct, and I'm glad that worked out for you. However I have heard stories about unreliability of that shuttle at times. If I were here for only 4 days I wouldn't want to waste any time waiting for my ride.

It CAN be cold. But January is off season for us. Restaurants and hotels offer great deals during that time of year. It's high season in Key West and as much as I love it, I avoid it during winter.

And I also agree with Gretchen. I lived in DC for years and highly recommend seeing it if you haven't. It can get cold there as well, but just wrap up.