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(raw_input())
for _ in range(t):
    n = int(raw_input())
    a = list(map(int,raw_input().split()))
    z = max(a)
    if(len(set(a)) == 1):
        print(-1)
    else:
        if(a.count(z) == 1):
            print(a.index(z)+1)
        else:
            f = 0
            for i in range(1,len(a)-1):
                if(a[i] == z and (a[i]>a[i-1] or a[i]>a[i+1])):
                    print(i+1)
                    f+=1
                    break
            if(f == 0):
                if(a[0] > a[1]):
                    print(1)
                elif(a[-1] > a[-2]):
                    print(len(a))
                else:
                    print(-1)