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.util.*;import java.io.*;import java.math.*;
public class Dominant
{
    public static void process()throws IOException
    {
        int n = ni();
        int[] a = nai(n);
        TreeSet<Integer> st = new TreeSet<>();
        for(int i = 0; i < n; i++)
            st.add(a[i]);
        if(st.size() == 1){
            pn(-1);
            return;
        }
        int val = st.last();
        int ans = 0;
        for(int i = 0; i < n-1; i++){
            if(a[i] == val && a[i+1] != val){
                ans = i+1;
                break;
            }
        }
        if(ans == 0){
            for(int i = n-1; i > 0; i--){
                if(a[i] == val && a[i-1] != val){
                    ans = i+1;
                    break;
                }
            }
        }
        pn(ans);
    }
   
    static AnotherReader sc;
    static PrintWriter out;
    public static void main(String[]args)throws IOException
    {
        boolean oj = System.getProperty("ONLINE_JUDGE") != null;
        if(oj){sc=new AnotherReader();out=new PrintWriter(System.out);}
        else{sc=new AnotherReader(100);out=new PrintWriter("output.txt");}
        long s = System.currentTimeMillis();
        int t=1;
        t=ni();
        //int k = t;
        while(t-->0) {/*p("Case #"+ (k-t) + ": ");*/process();}
        out.flush();
        System.err.println(System.currentTimeMillis()-s+"ms");
        out.close();
    }

 
    static void pn(Object o){out.println(o);}
    static void p(Object o){out.print(o);}
    static void pni(Object o){out.println(o);out.flush();}
    static int ni()throws IOException{return sc.nextInt();}
    static long nl()throws IOException{return sc.nextLong();}
    static double nd()throws IOException{return sc.nextDouble();}
    static String nln()throws IOException{return sc.nextLine();}
    static int[] nai(int N)throws IOException{int[]A=new int[N];for(int i=0;i!=N;i++){A[i]=ni();}return A;}
    static long[] nal(int N)throws IOException{long[]A=new long[N];for(int i=0;i!=N;i++){A[i]=nl();}return A;}
    static long gcd(long a, long b)throws IOException{return (b==0)?a:gcd(b,a%b);}
    static int gcd(int a, int b)throws IOException{return (b==0)?a:gcd(b,a%b);}
    static int bit(long n)throws IOException{return (n==0)?0:(1+bit(n&(n-1)));}
    static long power(long k, long c, long mod){
        long y = 1;
        while(c > 0){
            if(c%2 == 1)
                y = y * k % mod;
            c = c/2;
            k = k * k % mod;
        }
        return y;
    }
    static final Random random=new Random();
    
    static void ruffleSort(int[] a) {
        int n = a.length; 
        for (int i=0; i<n; i++) {
            int oi=random.nextInt(n), temp=a[oi];
            a[oi]=a[i]; a[i]=temp;
        }
        ArrayList<Integer> lst = new ArrayList<>();
        for(int i : a)
            lst.add(i);
        Collections.sort(lst);
    }

    static void ruffleSort(long[] a) {
        int n = a.length; 
        for (int i=0; i<n; i++) {
            int oi=random.nextInt(n);
            long temp=a[oi];
            a[oi]=a[i]; a[i]=temp;
        }
        ArrayList<Long> lst = new ArrayList<>();
        for(long i : a)
            lst.add(i);
        Collections.sort(lst);
    }
 
/////////////////////////////////////////////////////////////////////////////////////////////////////////
 
    static class AnotherReader{BufferedReader br; StringTokenizer st;
    AnotherReader()throws FileNotFoundException{
    br=new BufferedReader(new InputStreamReader(System.in));}
    AnotherReader(int a)throws FileNotFoundException{
    br = new BufferedReader(new FileReader("input.txt"));}
    String next()throws IOException{
    while (st == null || !st.hasMoreElements()) {try{
    st = new StringTokenizer(br.readLine());}
    catch (IOException  e){ e.printStackTrace(); }}
    return st.nextToken(); } int nextInt() throws IOException{
    return Integer.parseInt(next());}
    long nextLong() throws IOException
    {return Long.parseLong(next());}
    double nextDouble()throws IOException { return Double.parseDouble(next()); }
    String nextLine() throws IOException{ String str = ""; try{
    str = br.readLine();} catch (IOException e){
    e.printStackTrace();} return str;}}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////
}