Maybe not the best depending on your taste but....
I say it is.
By far the creepiest/scariest. Has the best stalker p.o.v. shots.
It has the best setting. The camp, woods and lake never looked as good in the later entries. Very atmospheric.
Easily the best ending with Jason popping out if the lake.
The soundtrack is well utilized and not overdone.
Realistic and well adjusted characters you sympathize for when they die instead of cheering for their inevitable demise.
Plus the mystery of who did it if you never seen it or any sequels before.