using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        List<string>[] col = new List<string>[]

        {

            new List<string>(){"aaa", "bbb"},

            new List<string>(){"a", "b", "d"},

            new List<string>(){"xy","sl","yy","aq"}

        };

        var ordered = col.OrderBy(x => x[0].Length).ToList();

        foreach (var list in ordered)

        {

            Console.WriteLine(string.Join(", ", list));

        }

    }

}