I loved both NY and California!
I'm pretty sure I answered on Astrid thread where I stayed in NY (atleast I remember reading it LOL). I stayed at the Pennyslvania Hotel, opposite Madison Square Garden. Very central, 5 minutes Times Square, 5 minutes Empire State (if you do nothing else, go up the Empire State...awesome - we did it twice, once in the morning and once at dusk), 5 minutes 5th Avenue, 10-15 minutes Central Station...you get the idea

The only thing that is a good distance away is the Financial District (minus the Towers now

) which is also where you go to catch the Statten Island Ferry (free, and takes you past the Statue of Liberty) or the proper paid for trips which take you to the Statue itself.
One thing to bare in mind. As a general rule, hotels in NY are expensive, they have totally lavish lobbies, and they have rooms that you can barely swing a cat in! Take it as being part of the city's character
I loved NY - and despite a reputation of NY'ers being brusk and rude, I found them to be just as nice and friendly as any other American I've met. They're just in a little bit more of a rush sometimes
Disneyland - well I haven't been there since the 2nd park and the Downtown Disney area opened, so it's changed dramatically! As Astrid says, many hotels are of the motel feel - unless you are staying onsite, then I say go for one of these and keep the cost down - there really isn't the same atmosphere that there is with WDW because Disney don't own a cushion of land around the parks like in Florida, so go for practical and economical. We stayed at the Carousel Inn, it is opposite DL Magic Kingdom and we watched the monorail go right by all the time, and could see the Matterhorn too. Just about all the hotels offer a shuttle to the park which saves you a mile long walk thru the car park to the gates.
DL is worth doing, but I wouldn't make a trip
just for the park (whereas I would make a trip just for WDW) but California has a great deal to offer and you'd be missing out if you went all that way and just went to DL. I didn't actually think much of LA, lacks personality I thought, but driving up the coast to San Francisco might be something to consider. SF is a FAB city - I just loved it, plus you go past San Simeon, Big Sur, Monterey (the best aquarium I have EVER been to, plus there is a factory outlet there if you feel the urge to shop, hehehe) and ooooh, oodles of things I haven't even touched on!
Whatever you pick, you won't go wrong IMO
