The country you grew up in almost always has a big quality-of-life head start, because it's where your friends and family are.
If you're in a poor country and changing country will get you a 10x increase in salary, that might more than compensate for only seeing your loved ones for a few days every few years. But if you're already pretty well off? Not so much.
The headstart is also in your customs. If you are used living w/o e.g. social security, a migration to the US is far more easy/interesting than when you are used to social security.
We could start listing things, but there's probably a list that someone else has made. And depending on how much weight/value they put on things, they could say one or the other is better.
I actually did, and visited the US many times after. I saw the good and the bad. In both countries.
There is no hard feeling, except that I want to express that the US while being a nice country to life is not the "pursue a better life" destination. It is all very relative.
Honestly the number one thing I miss about America is the big supermarkets and sheer diversity of food products available. Also much better restaurants on average.
Germany is generally a better place to live if you have a low to average income. Think everything from transit to health care to tenants' rights. But like if you're aiming for really high salaries as a software developer, America is the place to be.
I haven't but from what I have gathered the U.S is in many ways more preferable than Europe.