UK&Europe vs. USA long term?

It would depend on your definition of "comfortable". I have studied, lived and worked across Europe, the UK and the US. My circle of friends encompasses people from all walks of life and different interests/lifestyles.

My views would be:

Social security/benefits
The European countries win this one. Regardless of your background, education, legal status, or outcome of the adjudication - your life is infinitely better in Europe if you fall on hard times. It may be a medical emergency, homelessness, long-term unemployment or some other crisis. In most EU countries you don't have to sleep under a bridge and society will take care of you.
While healthy, young, intelligent, employable people don't have to worry about this for now - you never know what life will bring in the future. Some people need this framework of benefits for themselves or their family members. It's a generational contract which doesn't exist everywhere.
And it isn't just for the hard cases. When you decide to start a family, you will normally get a lot more in return in Europe.

Money/comp
Generally speaking, the US wins the race for the overall highest compensation (potential). It's because a lot more of personal expenses would have to be covered by the individual/family. Specific parts of life are more expensive in the US and "not free at source", i.e. health insurance, children/nursery, certain life events, education, ..
Life may seem "less expensive" if you purely focus on fantastic consumer deals online, Amazon or Harbor Freight (omg, products are so much cheaper in the US). But if your child needs a nursery that costs hundreds of dollars per month and you need a family fund so they may attend college one day - you don't really save in the long run.
While cars in the US are generally more affordable than in Europe, due to a lack of public transportation, higher mileage, gas, maintenance, distances, higher insurance costs, and rougher climates than in Europe - you also need many more cars throughout your life in America (after a decade of driving a used car in London and the SE of England, I still haven't done more than 2,500 miles per year).

Quality of life/standard of living
This depends on the individual situation. Some places in Europe have a high and amazing quality of life, mainly Scandinavian countries, Netherlands/Benelux, Switzerland, Germany, (..). Stuff there just works, roads are less broken, power outages won't happen or rarely, connectivity is there and internet is fast, public transportation is affordable and (almost) runs on time, public services are available to the public, and the general public enjoys many more benefits.
You can have some of these aspects in the US also, but they may require a city that is managed well and also an area with higher income.

Employment opportunities
This is highly dependent on the industry, location, era, and economic outlook. It's bad everywhere at the moment.
But, very generally speaking, I always thought of the US as a place with more opportunities. It's a bigger economic market, with more companies, people and, under normal circumstances, a stronger employment market.
Within the EU, there are many wonderful job markets in each nation. But all these markets are still different countries with different languages and different cultures and requirements. Not every single job in the EU is truly available to every EU citizen. An an example, a previous market (the UK), just exited for everyone else without a visa. While, in the US, a person in Hawaii could in theory move to NYC tomorrow morning, speak the same language and enjoy most of the rights as before. 
A similar move from Portugal to Sweden wouldn't be the same thing, although possible.

Infrastructure/technology/natural disasters
Basic infrastructure is better in Europe, in my opinion. Power lines are underground (except in parts of the UK and some nations), internet is relatively cheap and available, cell phone plans are much cheaper in Europe, roads are well maintained in some nations and "acceptable" in others, technology either comes from Europe itself or is accessible to most. It's no Japan, but you can get most things that are generally expected at an affordable price. With the "Americanization" of the ecommerce landscape, you will benefit from many services you didn't have two decades ago. American tech companies are really good at rolling out their services at scale and I am blown away how my Amazon account works seamlessly in Germany, California, London but also Switzerland.
With the exception of some inconvenient floods and a brief heatwave, European life has no tornadoes, no FEMA app warnings, and no wildfires that cross state lines.

It's not that the US is bad at these things, but there were more "issues" whenever I am in the US. Either a power line comes down on a highway, or a street is suddenly washed out. I am happily accepting of these small problems for a much nicer geography though, I find the  US has more diverse landscapes that are way more beautiful. It takes a lot more effort and money to keep a huge country working than a small European nation.

Social values
This is very different in each nation. There is no way you can compare a conservative state in the US with a liberal, agnostic Scandinavian country. Each individual should consider their personal values and how they match or differ from the destination.
A truly religious person with more conservative family values, possibly with the wish to express and defend their personal rights might feel more at home in the US. Europe is a collection of wonderful Christian nations, but Europeans are normally less vocal about their faith or personal values than Americans. Rights are given to Europeans, but they are, again, less vocal about demanding or defending them.

Happiness? Freedom? Rights?

America
The land of larger homes, larger roads, bigger cars, better income (in theory), and with better customer service have a lot of people "show happiness" in public. In America it is easier to connect with complete strangers, there is a mindset that "anything is possible" - maybe the last truly "free" country in the world with the everlasting "American Dream".
This country is among the few places where you might feel "at home" from the first moment you step off the plane. Regardless of your race, faith, mindset, and values - there is an underlying fabric of community and belonging. You are part of something bigger and are encouraged to work hard to achieve your goals. Success is celebrated and winners are the role models proving even you can make it one day if you only work hard enough.
Even though there is more political and social discourse in recent years, the majority of Americans still believe that United We Stand & Divided We Fall.

Europe
There is no comparable "European Dream". Most EU nations are about achieving a higher quality of life and better standards for everyone, not just the top percentile. Many elements of life are "given to you" at no cost at source, with the expectation that you will contribute and give back later in life. This is a fantastic place if you don't need to go from "rags to riches", if you don't need to achieve millions in a few years, if you don't need to become the CEO of a company you joined as an intern. All of this is still possible in the EU, just less likely. Europe is the home of the literal "middle class", but there are also stark differences among these limits within Europe. The gap between the lowest and highest salary is much bigger in London than in Stockholm.

My conclusion

I live in and love both Europe and the US. But I disagree that a person can be 100% agreeing with all the varying mindsets, beliefs, values and frameworks. Eventually you would have to make a decision for yourself which place to call home, the location where you will buy a forever home, with which mindset your children are raised, and which rights are important to you. I have seen many European friends make the leap to live and work in the US - most gave up and returned to their home nations. Not because the US is a bad place to be, but because many values may not be compatible with what they grew up with.
Also, I have shown the US in a relatively positive light here - but I also understand that it takes a lot to live a privileged life in America. If you are not among the lucky ones who are healthy, educated, intelligent and employable - you might not be the beneficiary of all the opportunities the nation has to offer...