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

# -*- coding: utf-8 -*-
"""
Created on Tue Oct 20 20:33:08 2020

@author: Dark Soul
"""

t=int(input(''))
for _ in range(t):
    n=int(input(''))
    arr=list(map(int,input().split()))
    find=0
    mx=max(arr)
    if arr.count(mx)==n:
        print(-1)
        continue
    if arr.count(mx)==1:
        print(arr.index(mx)+1)
        continue
    ans=-1
    
    for i in range(n):
        if arr[i]==mx:
            if i==0:
                if arr[i+1]!=mx:
                    ans=i
                    break
            elif i==n-1:
                if arr[i-1]!=mx:
                    ans=i
                    break
            else:
                if arr[i-1]!=mx or arr[i+1]!=mx:
                    ans=i
                    break
    if ans==-1:
        print(ans)
    else:
        print(ans+1)
            
    
        
        
        
    
        
    
            