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 i in range(int(input())):
    n=int(input())
    x=list(map(int,input().split()))
    if len(set(x))==1:
        print(-1)
    else:
        c=max(x)
        if x[0]==c and x[1]!=c:
            print(1)
            continue
        elif x[-1]==c and x[-2]!=c:
            print(n)
            continue
        for i in range(1,n-1):
            if x[i]==c:
                if x[i-1]!=c or x[i+1]!=c:
                    print(i+1)
                    break
