I will be brief, since arguing rarely serves faith.
We are commanded to repent and believe the Gospel and be baptized. A Sinner's Prayer is just a bunch of words if not prayed in sincerity and faith. All a Sinners Prayer does is to lead you verbally to pray to God what is in your heart, that you repent of your sins and confess Jesus Christ as the Son God who died on the Cross and shed his blood for your sins, and that God raised Jesus from the dead by the power of the Holy Ghost, as is commanded in Romans 10:9. Then, you are commanded to be baptized.
Let me also say, that if baptism is accompanied by sincere repentance then that is one and the same thing.
Many have attacked me by saying that the Sinners Prayer is not in the Bible. Oh yes it is. The heart of that prayer is your repentance and confession of faith in Jesus, mentioned over and over again. If water alone could save you, then why are we told that we must be born of water and of the Spirit? And why did Peter say that baptism is "not the putting away of the filth of the flesh, but the answer of a good conscience toward God"?
So what's the problem? Believe, repent, confess, and be baptized. I'm a simple guy; that seems simple enough to me.
I could go on and on, as could many detractors, most of whom simply argue semantics and not substance, or tout their perspective of how they read into certain Scriptures (and ignore others). I am not interested in debate. You can believe what you choose, but personally, I rather read the Bible and let God lead me, than listen to what everybody else says and then pick the theory I like the best. Ask God to show you, and when He does, then you will know from His hand and not someone else's.
My bottom line is that the Sinners Prayer really works. I have seen literally thousands of souls come to the altar and be dramatically transformed by the Spirit of God by that prayer. Not only could I watch as their entire facial expressions melt under the anointing, but you could feel the Holy Spirit come down just kneeling beside them. Countless brothers and sisters in the Lord will tell you that it is a supernatural experience that you never forget when you feel the weight of sin lift off your shoulders and the Spirit of God actually come inside your heart.
How can you argue with that? If the Spirit of God does something you don't agree with, why argue with it? Peter saw the same thing in Acts 10, and he sure didn't try to argue with it.
And please, don't accuse it of being something demonic, because that's treading really close to blasphemy of the Holy Ghost. If you don't agree, that's fine, but since you didn't create the universe, don't be so pompous that you are necessarily infallible and allow your mouth to cause you to cross a line that you can't come back from.
By all means, be baptized in water. I'm all for it. But why deny the experience of a supernatural conversion between God and a sincere, repentant sinner? How can you tell God that He is wrong for pouring out His Spirit and giving a desperate soul such an extraordinary salvation?
It seems to me that our time would be better spent witnessing to the lost than attacking the saved.