All who are born again by the Spirit of God are true Christians according to the Bible.
Romans 8:9 But you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you. Now if anyone does not have the Spirit of Christ, he is not His.
Ephesians 2:17 And He came and preached peace to you who were afar off and to those who were near. 18 For through Him we both have access by one Spirit to the Father. 19 Now, therefore, you are no longer strangers and foreigners, but fellow citizens with the saints and members of the household of God, 20 having been built on the foundation of the apostles and prophets, Jesus Christ Himself being the chief cornerstone, 21 in whom the whole building, being fitted together, grows into a holy temple in the Lord, 22 in whom you also are being built together for a dwelling place of God in the Spirit.
None of those are true. Some reject the truth that Jesus is God, and some reject the only true Gospel of Jesus Christ. Get away from them all.
The truth is that Jesus is God, and Jesus loves you so very much! Salvation is ONLY by believing in Jesus alone to save you, without adding ANY of your own works (John 3:16, John 6:29).
The truth about Jesus is that the only way to be saved and to get into heaven and avoid being sent to eternal hell, is by believing in faith alone that Jesus, who is God, died on the cross for all our sins as FULL PAYMENT for all our sins, and then Jesus rose from the dead (1 Corinthians 15:1-4). Believe in Jesus alone for salvation, and you will be in heaven, no matter what!
Salvation is a FREE GIFT that happens in a split second when you believe in Jesus alone to save you! It is impossible to lose or "leave" salvation (John 6:39-40, John 10:28, 1 John 5:13).
Please pray now: "Jesus, please forgive me of my sins. I believe that You died on the cross for my sins and You rose from the dead. Thank You for eternal life!" You will be in heaven with Him forever when you die!
I think any "ism" is subject to human dogma. I prefer to go directly to Christ. I agree with McGee...
My friend, if you have a religion, I suggest you get rid of it and exchange it for Christ. I personally do not think one can call Christianity a religion. There is no ritual whatsoever given with Christianity. Have you ever stopped to think of that? This is the reason we can have all kinds of churches with different forms of worship -- for instance you can sing the Doxology if you want to, but you don't have to. Christianity was never given a form to follow. Why? Because Christianity is a Person. To be a Christian means that you trust Christ. Religion has never been very helpful to man.
?J. Vernon McGee's Thru The Bible
Don't get me wrong...I also believe it is better to worship and fellowship with Christians than just being by myself. And I love singing old hymns. And there are some really good sermons to be heard. But I don't pay much attention to dogma.
Authentic Christianity is found in the individual, who may be part of those corporate entities, or not. Belonging to those denominations is not a guarantee or evidence of anything. Thanks for asking.
"true Christianity", as in followers of Jessi's teachings died out in the first century CE -- what remain is a hollow shell build around the teaching of Saul/paul
The Jehovah's Witnesses are a cult denying the Deity of Christ and His eternal being. They are not Christian, but only use the name of Christ to gain control over people and dependence upon their organization. They would like to sell you literature though.
Protestants are the ones practicing Christianity the closest to ancient Christianity, with their doctrines of justification by faith alone and Scripture alone as the final authority of faith. These doctrines are both clearly taught in Scripture and do not need a church to interpret it correctly..
Well, the best way to find out would be to listen to what Jesus himself said would be identifying characteristics of true Christians:
John 13:35 - "By this all will know that you are my disciples, if you have love among yourselves."
-----Who has love among themselves? Which group transcends racial and national boundaries, as a unified brotherhood in over 235 lands? Who refuses to kill their neighbors and fellow believers in war?
John 17:17 - "Sanctify them by means of the truth; your word is truth."
-----Which group adheres to the Bible as its authority, rejecting man-made doctrines that are not in harmony with the Bible, such as immortality of the soul?
Matthew 4:10 - "Then Jesus said to him: 'Go away, Satan! For it is written, "It is Jehovah your God you must worship, and it is to him alone you must render sacred service."??
John 17:6 - ?I have made your name manifest to the men you gave me out of the world. They were yours, and you gave them to me, and they have observed your word."
-----Which group worships only Jehovah God and makes his name known?
John 3:36 - "He that exercises faith in the Son has everlasting life; he that disobeys the Son will not see life, but the wrath of God remains upon him."
-----Which group accepts Christ Jesus as God's means of salvation, AND believes that obedience to him is essential for everlasting life?
John 18:36 - "Jesus answered: 'My kingdom is no part of this world. If my kingdom were part of this world, my attendants would have fought that I should not be delivered up to the Jews. But, as it is, my kingdom is not from this source.'?
-----Which group remains no part of this world, no part of its politics and conflicts?
Matthew 24:14 - "And this good news of the kingdom will be preached in all the inhabited earth for a witness to all the nations; and then the end will come."
Matthew 6:10 - ?Let your kingdom come. Let your will take place, as in heaven, also upon earth.?
----Which group is actively involved in preaching about God's Kingdom and what it will do for mankind on earth?
If we use Jesus' words as the guideline for determining who his true followers are, which we should, the answer to your question would have to be Jehovah's Witnesses.
So which one is the true Christianity: Eastern Orthodoxy, Roman Catholics, Protestant
Salvation is ONLY by believing in Jesus alone to save you, without adding ANY of your own works (John 3:16, John 6:29). 
