Berserk is highly regarded in the manga world, but whether it's the 'best' is subjective. It has a dark and intense plot that appeals to many, but not everyone might agree it takes the top spot. Different people look for different things in a manga.
At the moment, there's no definite information on whether Berserk manga will continue. It might, but it could also remain unfinished. A lot depends on the circumstances and decisions of those involved in its production.