Yes I know there are millions threads like these. But which is the best?
I'm very loyal to NCR so I could take away Legion and House. But can I be nice to NCR even if I have Wild card?
And can every gangs, tribes. From Power gangers to BoS and etc join you if you choose wild card?

It depends on what are your Courier's ideals and morals. There is no "right" way to reach the ending, just go with your character's ideas!

You can't follow the Wild Card and the NCR path: once you reach a certain point, the NCR will not like the fact that you're working with Yes Man. And it makes sense, because you'd be gathering assets that they want for the war. You can, however, be in an amicable (or at least neutral) relationship with the NCR even if you go Wild Card, provided you don't actively work against them.

The Wild Card path does include the option to enroll the help of other factions, though not every one you meet in the Mojave. You will be told which ones you can work with.

My favorite ending is Wildcard with as high NCR rep as possible, but there really isn't any objective best way to go.

And no. BOS will only ever ally with NCR, and the Powder Gangers will continue being Powder Gangers unless you wipe them out.

Which is the best...

NCR = Communism/ socialism
Legion = Slave Drivers/ sixist b*stards
Brotherhood = Keep the dangerous toys away from society cuz they already nuked the planet
Followers & The Kings = help who they can, freewill as long as you don't mess with others
Fiends, Khans & Powder Gangers = drug addicts & dealers

IMO only of course.

How did you arrive at the conclusion that the NCR is Communist or socialist?