Solar has been making incredible progress, and works in sunny locations, but it's not a general purpose solution. Nuclear is getting there, but it's still too expensive and over regulated. I can't say much about wind as I haven't looked into it enough to say. Both thermal and hydro are location dependent, so good when it works but not a general purpose solution.
So that leaves coal and natural gas. We have a lot of both, but switching over to natural gas to coal by retrofitting existing power generation would make a massive difference imo.
At the end of the day, we want diversity in the power grid, not just one thing for every place, since every place is different/has its own history.