Any newer military and many civilian weapons would be considered a great improvement over the M1, but during WWII the M1 was the best rifle for the regular troops.
I think it would still be a formidable weapon in the hands of someone who knew how to use it. The M16A2 has a 30 round mag which seem like a decisive advantage but if you were for example, a resistance soldier fighting against a tyranical government, you would likely be engaging troops from as far away as possible and you, very likely, would be firing no more than 8 rds before breaking contact and moving to a new position. Ammo availability is worth considering as well. We have seen how fast the NATO rounds can disapear from the shelves but, throughout all of that, rounds like .270, .243, 22-250, and 30/06 remained available.