Just go join one that has a presence near you enough to actually participate and see if it fits you.

The one doing the most work locally near you.

The girl reading this

I'm not american but in my opinion the PSL seems to be doing the most, at least from my vantage point, despite their huge amount of flaws

What is your criteria for best?

The one you can actually join.

If you're in a large city, and have choices, my recommendation is FRSO. They are not a party, but kind of function as one. It will make more sense when you read about them and talk to a member. You can DM me and I can give you more information if you're interested.

It is true, what diegeticscream said about not one party winning the revolution at the end of it. It's going to be the masses, first and foremost, and many parties will likely come together or spar when the time comes. Just due to the nature of the US's consciousness, or lack thereof, there will not be a dominant workers party here in the US for a long time. Longer than we have to carry out a revolution before a total fascist descent and climate change destroys everything. So it's going to be mass organizations that veer more radical under leadership of communists who work with the people, not an explicit communist party. At least, that's what I've picked up in my 6 months of organizing. I might revise that as time goes on.

My answer still remains the one you can actually join. Just get off your cheeks, every little thing counts. Even a conversation. Sure, it's not material the way we think of it, but those words are creating some kind of thought process in another's head, which may lead them to venture and learn more and become a great communist one day. That's how we all got here, no? Didn't just wake up as a tankie. Qualitative changes only come after many many quantitative ones. Those quantitative ones have to be built by us. So do SOMETHING and do not get discouraged when you're months in and haven't changed much. The one you can actually join and participate in is the best party for you.

That's not to say there isn't a "best" ML organization in the US, and for that my answer is also unchanged, I say FRSO.