Beba, here's something that will help you in planning, if you decide to go to the Met... it's the web page for their permanent collections:

http://www.metmuseum.org/Works_of_Art/collection.asp

Just click on any area (European Painting, or Egyptian, etc.) then click on "Collection Highlights" which will be largely shown in chronological order. See what appeals to you, and pick a few areas of interest. You'll get a map when you get there so you can easily navigate your way around.

By the way, you mentioned liking photography, and there's a very nice photography collection there.

NewbE, you're right about crowds, which is why I mentioned going as early in the morning as possible... but I don't think I've ever visited a wonderful site, in all my travels, that wasn't crowded -- great things are crowded for a reason I live in a large metropolitan area, so maybe I'm someone who can easily overlook crowds. Anyway, even though there are people around you, I've found that in most museums people are quiet and courteous in the exhibit halls. Just not a reason to miss one of the best museums in the world, in my opinion! Yes, I said it... in the world

The Metropolitan Museum of Art and the recently renovated MOMA (Museum of Modern Art)

No contest .. the Metropolitan Museum of Art must be your #1 destination.

Throw in the Frick if you'd like, but it's not comparable in any way, and you can see it's small collection quickly.

If you go to the MET, keep in mind that the admission charge is a "donation," and that you need not "donate" the full amount suggested.

Also, though I lived in NYC for many years, I was frustrated when I visited the MET a few months ago because several of the exhibits were closed and there were many detours in getting from place to place.

Therefore, get a floor plan at the information desk and ask which passage ways are closed.

Select two or three exhibits you want to see and prepare to be overwhelmed.

The salad bar in the main dining area is a pretty good deal considering you are in NYC and the MET.

The Met! I agree with Gekko, the Met, hands down. The point of your post is that you want one "hit you in the face" NY museum, and that's the Met. Who cares if its overwhelming...that's the whole point. Go in, get a floor plan at the information desk, pick a few exhibits you want to see (be sure to include the Temple of Dendur, and Tiffany windows) and go. You'll be amazed by the building, let alone the exhibits.

Without a doubt choose the Met. But go to the web site in advance and pick 2 or 3 departments that you want to see. Doing the whole thing would take a couple of days - and frankly there are parts that don't interest most people - and favorites that many people love. (Even at the age of 5 my brother used to love Arms & Armor and the Egyptian department - he wanted to get into the sarcophagi to see the mummies!)

To get the most out of it, see if you can take one of the gallery talks - to help you appreciated what you're seeing much more.

The Metropolitan Museum of Art.

It is encyclopedic spanning 5000 years whearas the other museums specialize in one thing (modern art, natural history, Jewish history, etc).

To miss the Temple of Dendur would be a crime.

Since you've indicated interest in photography, you should go MoMA. Its collection and presentation are without parallel. I am always wary when museums do extensive remodelling, but MoMA has pulled it off brillantly (twice). The collection is great and it's much more focused than the Met's. MoMA is definitely worth the $20 they charge, which is saying a lot.

I know you said 1 museum but why not kill 2 birds w/1 stone-go to the Met when it opens(9:30am I believe), preview it ahead on its website(listed above) so you know ahead what you want to see, then get to the Frick for at least 11/2 or 2 hours to see it all-they are only blocks from each other on Fifth Avenue-you can walk(but don't as will be tired from the Met) or take a cab or the downtown bus-given their proximity to each other, get the best of both worlds. Good luck

P.S. The Frick also has its own website

Just a tip for the novice art museum-visitor (no mattter which museum you choose)... I always find it really helpful to rent an audioguide. Since I'm no art historian myself, it's really worth it to hear the explanation of the key works of art and understand why those pieces are such a big deal. Usually the audioguide sends you to the most important works in the collection, and allows you to skip over any parts that aren't of interest to you. I have found that the couple of bucks spent on the guides really enhances my museum visit so is a great investment.

Thank you to everyone for their very insigtful comments! I truly feel more confident now that I shall go to the Met. For my first experience in a large museum I might as well see one of the best there is, right? And I will love the experience of being there and seeing the crowds will just be part of that experience. I will go early as some have suggested and I think I have narrowed my choices down to the costumes exhibit, the Egyptian exhibit, and the European masters exhibit. That will get me started until my next trip to NYC. Thanks also for the audioguide tip, and also for lunch ideas too. Thanks again everyone.

Don't miss the armor collection, the tiffany room and the sculpture garden. To me, they are the more relaxing areas of the Met. Also, I love the Rockefeller collection of South American and South Pacific art and canoes.

I disagree with previous posters. For my first time at the Met, I had no particular plan and enjoyed being surprised with each individual room.

Also, beba, if you are at the Met in late November, the Christmas tree might be up in the medieval gallery. The tree has many angels and is surrounded by Neopolitan creche figures.

Beba,
Just curious: If you're going to be there five days and only plan to go to one museum, what will you be doing the rest of the time? Is this a work trip, a family visit or vacation? You really should try to get to more than one. Besides the Metropolitan, the Museum of Natural History is one of the best in the world. Visiting NY and not seeing the Met or Natural History museums would be like going to Paris and missing the Louvre. Remember, you don't have to cover every inch of the place. It's OK to go for just two hours.

Much of the Met's American Wing, including its sculpture garden, is closed until 2009. The small cafe in the garden has been moved to the Grand Balcony.

andrews98682 my 5 days in NYC is purely vacation for a friend and I..Just a getaway to see something new . What do I plan on doing with the other days?
Well, the usual I guess, ESB,Statue of Liberty, a ferry ride, the Radio City Music hall Christmas Spectacular, a morning bus tour of the city, maybe a live taping of a morning show (if I get the tickets)2 or 3 Broadway shows(2 for sure and 3 if possible), some shopping, some wandering through Central Park, some walking in East and West Sides,So Ho ,Greenwich Village,Little Italy,maybe Chinatown (probably not) a nighttime stroll through Times Square, a visit to Grand Central Station ( a must for me because I use the expression a lot!!)and then of course a museum. So I think I will be fairly busy, but I hope to have some time to sit and 'watch' the city and New Yorkers in general. Even though that might sound like a lot of ground to cover I don't want my vacation to be rush rush rush, but yet strike the happy balance of seeing a lot, but yet still 'feeling' a lot.Do you have any suggestions to do this differently?

Sounds like a good plan. If you have time, I would suggest adding another museum. Some of the things you plan to do won't take that long (like Grand Central) or can be done at night. Also, you could do the museums (Met, natural history) and Central Park (If you like zoos, they have a good one. It's much smaller than the Bronx Zoo and takes about two hours to see).