I think that i have many favorites cities. I havent' traveled all that much, but have yet to travel someplace where i felt "meh". yes, there are better and there are boring but i have always found it exciting to be someplace "else", to visit local museums, supermarkets, to go on local public transportation, eat a local delicacy, etc. and to me - it doesn't really matter if it's someone else's favorite or if people say "boring". a few years ago i had an opportunity to fly form the US to israel through Milan, and had a whole day in the city. people had said to me "milan? once you see the duomo and have a cup of coffee, that's the whole city." well, guess what - i had a great day. i took a train ride about 40 minutes outside the center of the city and explored an ancient walled city (i was lucky because I had someone that i knew from 100 years ago who lived there but still). and if i hadn't gone there, i would've found something else to do. I went once to bodrum, turkey, (with a group) and we spent one day on the island of Kos , even though the organizers said "it's boring". but again, guess what - it was beautiful, it was different, we had a great time.
so bottom line - the "favorite city" is what YOU make of it.
now, disregarding all that - I love NYC. there is really something for everyone. the city has a special vibe, it's trendy and lively and amazing. it has gazillions of museums, from the amazing metropolitan and MOMA to tiny obscure institutions. gourmet and expensive restaurants to cheap delish street food. Fancy fifth avenue boutiques (think that scene in Pretty Women "we don't have anything here for you") to 5$ I heart NY t shirts. music, amazing architecture, parks and waterways.