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())
    nums = [int(i) for i in input().split()]
    max_ = max(nums)
    c = nums.count(max_)
    if c == 1:
        print(nums.index(max_) + 1)
    elif c == n:
        print(-1)
    else:
        for i in range(n):
            if nums[i] == max_:
                if i > 0 and nums[i - 1] < max_:
                    print(i + 1)
                    break
                if i + 1 < n:
                    if nums[i + 1] < max_:
                        print(i + 1)
                        break
