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

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class DominantPiranha {				//1433C        
	
	public static void main(String[] args) throws NumberFormatException, IOException {
		
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int t = Integer.parseInt(br.readLine());
		StringBuilder sb = new StringBuilder();
		while (t-- > 0) 
		{
			int n = Integer.parseInt(br.readLine());
			StringTokenizer st = new StringTokenizer(br.readLine() , " ");
			int a[] = new int[n];
			int mx = Integer.MIN_VALUE;
			for (int i = 0; i < n; i++) {
				a[i] = Integer.parseInt(st.nextToken());
				mx = Math.max(mx, a[i]);
			}
			sb.append(solve(a, n, mx)).append("\n");
		}
		System.out.println(sb);
	}

	private static int solve(int[] a, int n, int mx) {
		
		int idx = -1;
		for (int i = 0; i < n; ++i) {
			if (a[i] != mx) continue;
			if (i > 0 && a[i - 1] != mx) idx = i + 1;
			if (i < n - 1 && a[i + 1] != mx) idx = i + 1;
		}
		return idx;
	}
}