Are these dice nontransitive?
Python 2, 269

Here's a nice little expression that evaluates to a function. It accepts three lists of integers. Passes all test cases.

lambda A,B,C,w=lambda A,B:cmp(sum(cmp(a,b)for a in A for b in B),0),x=lambda A,B:cmp(sum(cmp(a+c,b+d)for a in A for b in B for c in A for d in B),0): (w(A,B)==w(B,C)==w(C,A)!=0)*((x(A,B)==x(B,C)==x(C,A))*["","strongly ","Grime-"][x(A,B)*w(A,B)]+"nontransitive")or"none"