Which American city would be most welcoming to me?

This is a question with no real answer. Most large us city's have a noticable immigrant population that everyones used to so any major city is as good as the next. Not only that but most people every where probably wouldn't care anyway assuming you don't move to the to backwoods Alabama or constantly talk about how the U.K. is better in your opinion. I personally wouldn't worry about.

New York

It won't matter a bit. You should be more concerned with where you can afford to live on your budget and what climate appeals to you the most.

Washington, D.C. has people from all over the world (and all over the country, too) and would probably be a comfortable fit. People are very accepting of one another.

What taxes have you ever paid to the US?

The city where you can get a job.

you probably DONT have a US passport ....you need to get a high end degree to get a job

Cities are inanimate objects, they cannot welcome anybody. Cities are occupied by people. Every city has lots of people who love Americans with a British accent, some that don't give a shi*t about it either way, and some who will point out that the wounds of 1776 are still fresh. So cover up the Union Jack that you have tattooed on your forehead, and you will look like anybody else and nobody will have to waste a second on trying to figure out if they want to like you or not.

This applies to all cities in the United States.

I suspect most people would ignore you. If you have a British accent, some might find it charming. I would prefer Daytona Beach, Florida. Most of the residents are from somewhere else. And visitors come in from all around the US and probably the world.

Austin, Texas tends to be pretty accepting of people around the world.