My mother and sister always use Virgin Holidays when they go to the US and swear by them for reasonable prices, scheduled Virgin flights and good (but not super-pricey), hotels.
I lived in NYC for six years and I can tell you this - NY hotels, particulalry ones in good locations, are very expensive - so a flight and hotel deal will nearly always work out cheaper. Beware hotels that appear cheap - they're probably nasty and/or in a terrible location.
I would go for 5-7 days. If you only go for 3-4 you're going to be jet-lagged for the first couple of days and you'll be too tired in the evenings to really enjoy yourselves and go out, which is a big part of the enjoyment in visiting NY. There is so much to see and do that you won't be bored.
I would go for a week rather than 3-4 nights if finances allow. Also NYC is vast and there's plenty to do.
Which UK airport would you like to depart from ideally?.
You would also need to pay for an ESTA for each of you prior to travelling; this is the US's electronic travel authorisation. The cost currently is $14 US (around £9 sterling) per person and is valid for 2 years from date of issue.
Look at the usual sorts of sites; Tripadvisor, expedia etc. Time difference is 5 hours behind UK time. Flight time is around 7-8 hours leaving the UK, it will be shorter in duration returning to the UK. That flight will be an overnight one arriving into the UK early the following morning.
So I'm looking to go 2014 Whit Holidays with my DH, DD15 and DS9. 1) which sites do you use? 2) should it be a flight/hotel deal or book separately - which sites 3) I think a week would be too long but what's the ideal - bearing in mind the time difference ( which I need to get my head around) 3-4 nights? Any advice you can give would be appreciated TIA