1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

t=int(input())
for i in range(t):
    n=int(input())
    A=list(map(int,input().split()))
    if(len(set(A))==1):
        print(-1)
    else:
        v=max(A)
        #for j in range(1,n):
        if(A.index(v)>0 and A.index(v)<n-1):
            print(A.index(v)+1)
        elif(A.index(v)==0):
            j=0
            while(A[j]==v):
                j+=1
            print(j)
        else:
            j=n-1
            while(A[j]==v):
                j-=1
            print(j+2)