I DNK, the "best" for me is an SKS with the original 10-shot mag.
Many prefer an AK or something else.
I'd say it's a very personal choice, depending on what your
selection paradigms for " best" are.
How much punch do you want a round to have VS portability?
Are you talking most accurate? Most actual "assault rifles" aren't
extremely accurate, because armies depend on massed fire or volley
fire to compensate for their hardware's deficiencies.
Are you looking for most dependable? Gonna get a few
Do you prefer sturdy, robust, and neglect resistant, and easy to clean?
Comblocs hold a distinct advantage.
Some AR owners here would take my favorite go to gun and
throw it right in the trash...