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

for _ in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    if a.count(a[0])==n:
        print(-1)
    else:
        #print(a.index(max(a))+1)
        idx=a.index(max(a))
        if idx!=0:
            print(idx+1)
        else:
            if a[idx+1]!=a[idx]:
                print(idx+1)
            else:
                c=0
                for z in range(1,n-1):
                    if a[z]==a[idx] and (a[z-1]!=a[idx] or a[z+1]!=a[idx]):
                        idx=z
                        c=1
                        break
                if c==1:
                    print(idx+1)
                else:
                    print(-1)

