If you're going from NW DC to Manhattan the Accela is usually faster door to door from DC, because you're going from Union Station to Penn, as opposed to going to National, going through security, and then arriving at the outskirts of NYC and taking a cab into the city.
It's also much more comfortable, and both the Accela and the regionals have a pretty good on-time percentage in on that route.
It's the only decent Amtrak route, but well recommended.
I live in Philadelphia and use Amtrak to go up to New York on the weekends, where I used to live. The train ride is actually faster than the most-distant points on the NYC subway, so in a way I feel like I'm actually in a distant part of the same city.
Anyway...the Northeast Corridor is great. Especially in the middle of the night when its cheap, and theres no traffic on the rails.
Yeah, and from Penn you can jump on the Subway and get most places in the city without too much fuss (though it might be hard to get luggage through the turnstiles with you).
Let's just say that it's appealing enough to be on my options list for travel whenever I go the NYC.
It meets airline carry-on requirements, but can be easily be slipped on and off in urban environments as needed. It probably won't work so well if you need to wear a suit jacket, but is otherwise great.
It's also much more comfortable, and both the Accela and the regionals have a pretty good on-time percentage in on that route.
It's the only decent Amtrak route, but well recommended.