New York & ?

torbrex

Having been to both Boston & Washington it would be difficult to recommend either over the other as they both have an awful lot to offer the walking tourist.
Both cities have great transport systems and getting about the major tourist sites is relatively easy and both cities also have a good selection of escorted tours.
Big plus for DC is free entry to all the major attractions and museums, big plus for Boston has to be the people, they are just so much friendlier and I also did a whale watching trip off Boston harbour which made for a WOW day
I visited both cities in late summer/early autumn and the climate was just right for me, if you take your camera, you will need extra storage for all the photos that you will take, I took over 800 in DC alone.

bluenoseam

The only thing i'd say is that depending on weather it might either get wet or get chilly in the North East - so keep that in mind. And it only takes about 1-2 hours on the train between NY & Philly, you can probably get there for less than $100 return each heading out earlyish (9.30) and returning in the evening.

Bah i wanna go back to the states!

rainbow_carnage

I've been to Boston and DC several times. Both are worth visiting. If you're into touristy things, DC has more of those, but you won't regret picking either one.

I'm less of a fan of Philly, but it's closer to NYC.

If I had to pick a second city to visit in that part of the world, I'd pick New Orleans or Chicago.

Indout96

I loved DC more than New York

Same here, we loved Washington, we loved Boston as well but TBH found it very small and having been will probably not go again as we have done everything there was to do.
On the other hand as someone else mentioned have a think about Toronto and Niagra Falls but if you do that then take a trip over to the US national park side (walk over bridge) as it is way nicer than the built up Canadian side