JObject.Parse vs JsonConvert.DeserializeObject

Question 1

The LINQ-to-JSON API (JObject, JToken, etc.) exists to allow working with JSON without needing to know its structure ahead of time. You can deserialize any arbitrary JSON using JToken.Parse, then examine and manipulate its contents using other JToken methods. LINQ-to-JSON also works well if you just need one or two values from the JSON (such as the name of a county).

JsonConvert.DeserializeObject, on the other hand, is mainly intended to be used when you DO know the structure of the JSON ahead of time and you want to deserialize into strongly typed classes. For example, here's how you would get the full set of county data from your JSON into a list of County objects.

class Program
{
    static void Main(string[] args)
    {
        string countiesJson = "{'Everything':[{'county_name':null,'description':null,'feat_class':'Civil','feature_id':'36865',"
                +"'fips_class':'H1','fips_county_cd':'1','full_county_name':null,'link_title':null,'url':'http://www.alachuacounty.us/','name':'Alachua County'"+ ",'primary_latitude':'29.7','primary_longitude':'-82.33','state_abbreviation':'FL','state_name':'Florida'},"+
                "{'county_name':null,'description':null,"+ "'feat_class':'Civil','feature_id':'36866','fips_class':'H1','fips_county_cd':'3','full_county_name':null,'link_title':null,'url':'http://www.bakercountyfl.org/','name':'Baker County','primary_latitude':'30.33','primary_longitude':'-82.29','state_abbreviation':'FL','state_name':'Florida'}]}";

        foreach (County c in JsonParseCounties(countiesJson))
        {
            Console.WriteLine(string.Format("{0}, {1} ({2},{3})", c.name, 
               c.state_abbreviation, c.primary_latitude, c.primary_longitude));
        }
    }

    public static List<County> JsonParseCounties(string jsonText)
    {
        return JsonConvert.DeserializeObject<RootObject>(jsonText).Counties;
    }
}

public class RootObject
{
    [JsonProperty("Everything")]
    public List<County> Counties { get; set; }
}

public class County
{
    public string county_name { get; set; }
    public string description { get; set; }
    public string feat_class { get; set; }
    public string feature_id { get; set; }
    public string fips_class { get; set; }
    public string fips_county_cd { get; set; }
    public string full_county_name { get; set; }
    public string link_title { get; set; }
    public string url { get; set; }
    public string name { get; set; }
    public string primary_latitude { get; set; }
    public string primary_longitude { get; set; }
    public string state_abbreviation { get; set; }
    public string state_name { get; set; }
}

Notice that Json.Net uses the type argument given to the JsonConvert.DeserializeObject method to determine what type of object to create.

Of course, if you don't specify a type when you call DeserializeObject, or you use object or dynamic, then Json.Net has no choice but to deserialize into a JObject. (You can see for yourself that your dynamic variable actually holds a JObject by checking jResults.GetType().FullName.) So in that case, there's not much difference between JsonConvert.DeserializeObject and JToken.Parse; either will give you the same result.

Question 2

JsonConvert.DeserializeObject has one advantage over JObject.Parse: It is possible to use custom JsonSerializerSettings.

This can be very useful e.g. if you want to control how dates are deserialized. By default dates are deserialized into DateTime objects. This means that you may end up with a date with another time zone than the one in the json string.

You can change this behaviour by creating a JsonSerializerSetting and setting DateParseHandling to DateParseHandling.DateTimeOffset.

An example:

var json = @"{ ""Time"": ""2015-10-28T14:05:22.0091621+00:00""}";
Console.WriteLine(json);
// Result: { "Time": "2015-10-28T14:05:22.0091621+00:00" }

var jObject1 = JObject.Parse(json);
Console.WriteLine(jObject1.ToString());
// Result: { "Time": "2015-10-28T15:05:22.0091621+01:00" }

var jObject2 = Newtonsoft.Json.JsonConvert.DeserializeObject(json, 
  new Newtonsoft.Json.JsonSerializerSettings 
  { 
    DateParseHandling = Newtonsoft.Json.DateParseHandling.DateTimeOffset 
  });
Console.WriteLine(jObject2.ToString());
// Result: { "Time": "2015-10-28T14:05:22.0091621+00:00" }

Question 3

For me the key difference I was interested in was Speed.

I made a simple test to find out if it was faster to use JToken.Parse(string) or DeserializeObject<JToken>(string) to create a large amount of JToken and these were the results after 2,000,000 iterations using a sample of real world data

Method	Operating System Ticks	Milliseconds
JsonConvert	86123945	8612ms
JToken	67671724	6767ms

There was some variation between runs but the difference was always large.

Here is the test so you can modify it or run it yourself:

    private static string s = @"{'stream':'btcusdt @bookTicker','data':{'u':20430107433,'s':'BTCUSDT','b':'21223.72000000','B':'3.29440000','a':'21223.73000000','A':'2.05450000'}}";

    private static Stopwatch sw = new Stopwatch();

    private static void Main(string[] args)
    {
        JToken convert = default;
        sw.Restart();
        for (int i = 0; i < 2000000; i++)
        {
            convert = JsonConvert.DeserializeObject<JToken>(s);
        }

        Console.WriteLine("JsonConvert: " + sw.ElapsedTicks + " [" + sw.ElapsedMilliseconds + "ms]");
        convert.ToString();

        convert = default;
        sw.Restart();
        for (int i = 0; i < 2000000; i++)
        {
            convert = JToken.Parse(s);
        }

        Console.WriteLine("JToken     : " + sw.ElapsedTicks + " [" + sw.ElapsedMilliseconds + "ms]");
        convert.ToString();

        Console.ReadLine();
    }

Question 4

I knew an advantage that JsonConvert.DeserializeObject can deserialize an Array/List json text directly, but JObject cannot.

Try below sample code:

using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System;
using System.Collections.Generic;

namespace NetCoreJsonNETDemo
{
    internal class Person
    {
        [JsonProperty]
        internal string Name
        {
            get;
            set;
        }

        [JsonProperty]
        internal int? Age
        {
            get;
            set;
        }
    }

    internal class PersonContainer
    {
        public List<Person> Persons
        {
            get;
            set;
        }
    }

    class Program
    {
        static T RecoverPersonsWithJsonConvert<T>(string json)
        {
            return JsonConvert.DeserializeObject<T>(json);
        }

        static T RecoverPersonsWithJObejct<T>(string json) where T : class
        {
            try
            {
                return JObject.Parse(json).ToObject<T>();
            }
            catch (Exception ex)
            {
                Console.WriteLine("JObject threw an Exception: " + ex.Message);
                return null;
            }
        }

        static void Main(string[] args)
        {
            List<Person> persons = new List<Person>();

            persons.Add(new Person()
            {
                Name = "Jack",
                Age = 18
            });

            persons.Add(new Person()
            {
                Name = "Sam",
                Age = null
            });

            persons.Add(new Person()
            {
                Name = "Bob",
                Age = 36
            });

            string json = JsonConvert.SerializeObject(persons, new JsonSerializerSettings()
            {
                Formatting = Formatting.Indented
            });

            List<Person> newPersons = RecoverPersonsWithJsonConvert<List<Person>>(json);
            newPersons = RecoverPersonsWithJObejct<List<Person>>(json);//JObject will throw an error, since the json text is an array.

            PersonContainer personContainer = new PersonContainer()
            {
                Persons = persons
            };

            json = JsonConvert.SerializeObject(personContainer, new JsonSerializerSettings()
            {
                Formatting = Formatting.Indented
            });

            newPersons = RecoverPersonsWithJObejct<PersonContainer>(json).Persons;

            newPersons = null;
            newPersons = RecoverPersonsWithJsonConvert<PersonContainer>(json).Persons;

            Console.WriteLine("Press any key to end...");
            Console.ReadKey();
        }
    }
}

Question 5

Apart from the answers provided here around usage, which are correct as per me : Jobject.Parse -> when the Json is not strongly Typed or you do not know the structure of Json ahead of time

JsonConvert.DeserializeObject<T> -> When you know which class or type to cast the Json in. T can be a complex class or a simple type

My answer is based on the performance in case where the structure is not known, as given in the OP code, if we benchmark the usage of both methods for performance, it is observed that Jobject.Parse() fares well in terms of allocated memory, please ignore the name of methods, I am first calling the method with 'JsonConvert.DeserializeObject' and then second method is with Jobject.Parse