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

from __future__ import division, print_function
import math
import os, sys
from sys import maxint
from io import BytesIO, IOBase

if sys.version_info[0] < 3:
    from __builtin__ import xrange as range
    from future_builtins import ascii, filter, hex, map, oct, zip


def ii():  return int(input())


def si():  return input()


def mi():  return map(int, input().strip().split(" "))


def msi(): return map(str, input().strip().split(" "))


def li():  return list(mi())


def dmain():
    sys.setrecursionlimit(1000000)
    threading.stack_size(1024000)
    thread = threading.Thread(target=main)
    thread.start()


# from collections import deque, Counter, OrderedDict,defaultdict
# from heapq import nsmallest, nlargest, heapify,heappop ,heappush, heapreplace
# from math import log,sqrt,factorial,cos,tan,sin,radians
# from bisect import bisect,bisect_left,bisect_right,insort,insort_left,insort_right
# from decimal import *
# import threading
from itertools import permutations

# Copy 2D list  m = [x[:] for x in mark] .. Avoid Using Deepcopy

abc = 'abcdefghijklmnopqrstuvwxyz'
abd = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, 'f': 5, 'g': 6, 'h': 7, 'i': 8, 'j': 9, 'k': 10, 'l': 11, 'm': 12,
       'n': 13, 'o': 14, 'p': 15, 'q': 16, 'r': 17, 's': 18, 't': 19, 'u': 20, 'v': 21, 'w': 22, 'x': 23, 'y': 24,
       'z': 25}
mod = 1000000007
# mod=998244353
inf = float("inf")
vow = ['a', 'e', 'i', 'o', 'u']
dx, dy = [-1, 1, 0, 0], [0, 0, 1, -1]


def getKey(item): return item[1]


def sort2(l): return sorted(l, key=getKey, reverse=True)


def d2(n, m, num): return [[num for x in range(m)] for y in range(n)]


def isPowerOfTwo(x): return (x and (not (x & (x - 1))))


def decimalToBinary(n): return bin(n).replace("0b", "")


def ntl(n): return [int(i) for i in str(n)]


def ceil(x, y):
    if x % y == 0:
        return x // y
    else:
        return x // y + 1


def powerMod(x, y, p):
    res = 1
    x %= p
    while y > 0:
        if y & 1:
            res = (res * x) % p
        y = y >> 1
        x = (x * x) % p
    return res


def gcd(x, y):
    while y:
        x, y = y, x % y
    return x


def isPrime(n):  # Check Prime Number or not
    if (n <= 1): return False
    if (n <= 3): return True
    if (n % 2 == 0 or n % 3 == 0): return False
    i = 5
    while (i * i <= n):
        if (n % i == 0 or n % (i + 2) == 0):
            return False
        i = i + 6
    return True


def read():
    sys.stdin = open('input.txt', 'r')
    sys.stdout = open('output.txt', 'w')


def main():
    for _ in range(int(input())):
        n = int(input())
        arr = list(map(int, raw_input().split()))

        def solve(arr, n):

            m = max(arr)
            index = []
            for i in range(n):
                if arr[i] == m:
                    index.append(i)

            if len(index) == n:
                return -1
            else:
                for i in index:
                    if i == 0:
                        if arr[1] != arr[i]:
                            return 1
                    elif i == n - 1:
                        if arr[-2] != arr[-1]:
                            return n
                    else:
                        if arr[i] != arr[i - 1] or arr[i] != arr[i + 1]:
                            return i + 1
                return -1

        print(solve(arr, n))



BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


def print(*args, **kwargs):
    """Prints the values to a stream, or to sys.stdout by default."""
    sep, file = kwargs.pop("sep", " "), kwargs.pop("file", sys.stdout)
    at_start = True
    for x in args:
        if not at_start:
            file.write(sep)
        file.write(str(x))
        at_start = False
    file.write(kwargs.pop("end", "\n"))
    if kwargs.pop("flush", False):
        file.flush()


if sys.version_info[0] < 3:
    sys.stdin, sys.stdout = FastIO(sys.stdin), FastIO(sys.stdout)
else:
    sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)

input = lambda: sys.stdin.readline().rstrip("\r\n")

# endregion


if __name__ == "__main__":
    # read()
    main()
    # dmain()

# Comment Read()