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 defaultdict
for _ in range(int(input())):
    n = int(input())
    a = list(map(int,input().split()))
    same = [a[0]]*n
    if(a==same):
        print(-1)
    else:
        large =-1
        index = 0
        for i in range(n):
            if(large<a[i]):
                large = a[i]
                index = i+1
        j=0
        if((index-1)==0):
            while(True):
                if(a[j]==large):
                    while(a[j]==large):
                        index = j
                        j+=1
                    break
                j+=1
            index=j
        print(index)