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 collections import *
from functools import *
import math
import sys 
 

inp = sys.stdin.readline
out = sys.stdout.write
 
def mi():
    return map(int,inp().split())
def li():
    return list(mi())
def ii():
    return int(inp())
 
def main():
    for _ in range(ii()):
        n = ii()
        a = li()
        m = max(a)
        f = 0
        for i in range(n):
            if a[i]<m:
                f = 1
                break
        if f == 0:
            print(-1)
        else:
            ans = 0 ; f =0
            for i in range(1,n):
                if (a[i-1] != a[i] and a[i] == m):
                    ans = i+1
                    f = 1
                    break
            if f == 1:
                print(ans)
            else:
                for i in range(n-1):
                    if (a[i] != a[i+1] and a[i] == m):
                        ans = i+1
                        f = 1
                        break
                print(ans)
main()
