It really doesn’t matter what the pros and cons are since, for all intents and purposes, it will never happen if OP remains as he is – unskilled, British, without a sponsoring employer and without an American spouse.
And he’s never even been here to see if he’d actually enjoy the experience.
Look, our cultures are different, our norms are different, our etiquette is different, etc. At least come visit a few cities you’re considering, preferably for longer than a week each, and just get a feel for the place. Pretend you live there – go grocery shopping, run errands, take public transportation, try to make some friends, experience the social life in a non-touristy way. You might love it; you might not.
You might discover you can’t stand NYC but do enjoy the small towns of upstate New York. You might discover that the pace of a West Coast city like Portland is much more comfortable than the East Coast pace. You might find yourself standing on a butte in Wyoming overlooking absolutely nothing as far as the eye can see, thinking, “This…now, this is the life for me!” You won’t know unless you visit first.
I hope you and all the others offering Ryan_Liam visit first advice are willing to sponsor him, because I’m guessing that visiting, and especially visiting and travelling about, might be a bit out of reach. Truthfully, I think Hello Again hit the nail on the head. R_L might be better off choosing somewhere in Canada, though I confess I know nothing of their immigration policy regarding UK nationals.
Anyone who can’t afford to visit someplace for a couple of weeks has no business moving there.
I think your best bet might be NYC as you don’t need a car here if you settle in one of the five boroughs. You can find a mediocre job and then find a one bedroom sublet in an interesting place like Astoria, Queens. You’ll have easy access to all that the region has to offer – NYC museums, cultural festivals, beaches and great food. But I’m not sure why you would want to do that for more than six months. NYC is one of the world’s most fascinating places but it is not easy to be poor here. You might want to try it for a few months but I don’t it would particularly improve your quaiity of life in the long term.
I think you immigrating to the U.S. is not likely. But you can look into commonwealth programs like a work visit program. My sister did that to work and visit Australia from Canada. It was more than ten years ago but maybe something like that would work. It did have an age restriction.
Another thing to consider: If you’ve an accent, you will always feel like an outside in the US, unless you surround yourself with ex-patriots.
It would be great if everyone who contemplated moving, especially moving to a different continent, were so fiscally sound. But it’s not always the case. Mr. Liam (if his fiscal situation is tight) would hardly be the first to take such a big gamble, spending his/her last penny to see if the grass really is greener on the other side. Hell, with that advice, the West might never have been settled. 
The West was already settled. The settlers might have figured that out if they popped by for a visit first.
Here’s a totally different perspective -
Don’t move to the US, for all of the obstacles that have been mentioned.
Instead, move to Canada.
As a UK person, you can work and live in Canada more easily than the US.
And it’s like the US, but not exactly like the US.
When was the last time a foreigner could pitch up to the US and just start working, legally, at blue collar jobs? Sounds like something from the 1920s.
Saying that, I have a couple of Irish friends who went over and worked on building sites and fishing boats around the Boston area in the 1980s. Not completely on the level IIRC, doubt many tax returns were filed, but they weren’t living off the grid or anything.
Less of everything.
If you are an unmarried, able-bodied adult male without children you get NO welfare other than, maybe, food stamps (which would require you to be a legal resident, which I don’t see happening unless you have a job). You are not guaranteed housing, healthcare, or anything else.
If you are the legal guardian of a child or children the lot of you would get food stamps, if the kids were young enough they might also get WIC, and a very small cash handout intended for the benefit of the kids, not you or your spouse.
That’s it for welfare in the US these days.
Well, that eliminates all of my ancestors…
While it is certainly possible to spend one’s last penny and enter a new country without money or other resources and later on become successful (however you define that) it’s a nasty, long slog and doesn’t always end well. A big risk. Most of my ancestors took that risk because the alternative was starvation (the Irish who came over in the 1860’s) or death (the Russians from 1900 to 1939). I certainly hope the OP’s situation isn’t that dire.
It would have eliminated my father’s side of the family.
It certainly won’t be easy even if Mr. Liam has a little nest egg set aside for relocation. Also, while I personally would open up the immigration doors to anyone (non-felon) who wants to come, it’s not my decision and we (the US) pretend like were an exclusive club now.
I’m not quite sure about this. English accents tend to be, as they say, “chick magnets”.
None of my English friends ever had problems dating here.
As for the expense of moving to NYC, of course it can be done. It’s just not as easy if you are not from here and do not have a person to turn to for help.
The other problem with the kind of work he can do is that these are the types of jobs going to part-time hours… Just enough hours to not have to pay for insurance.
Not to be too much of a downer, but this first person account of trying to immigrate to the US would probably be a good thing for you to read
I’d like to ask the OP.
How much of your original nationality do you want to keep and how much “American” do you want to be?
For example, we have people here who have been living here 5-10 years or so who are totally Americanized and you cannot detect a bit of foreign accent in their language or customs. On the other side are people who never integrate, live totally in ethnic enclaves, and hardly speak a word of English.
Most people though are mixed. They join clubs of other ex-pats to keep up their language skills and teach them to their children.
So how much?
I suggest living in a state that has water. Anywhere east of the Mississippi will do. If you won’t be making a lot of money, I would go for a middle sized city, perhaps a university town.
I would note that the person in that article was a highly skilled migrant with an advanced professional degree, extensive work experience in the US and very, very many ties to the US. And it was still impossible.
OP is living in a delusion that he can immigrate to the US when he can’t.
And yet, loads of folks arrive from the south, without the benefit of being able to speak a little bit of English, and manage to make it despite of legal roadblocks. Seems like what is really needed is wit and tenacity.
I’d be curious to know why they would have an advantage over a Brit who, frankly, doesn’t bring a whole lot of negative, suspicious baggage in his accent or skin tone.
ETA: No snark intended, by the way. I’m genuinely curious about that.
“Some make it” occurs by sheer numbers. There are something like 6 million Mexicans in the US illegally, just rolling the dice a very few will make it big, some will do well, most will not.
Also consider that around 300-400 of those illegal immigrants die each year while crossing the border.
It’s one hell of a lottery. Yes, wit and tenacity count but if your coyote locks you into a railroad car you get to die a gruesome death on a railroad siding. As just one example. There are many others.
They have no advantage over a single Brit, other than sheer numbers.