I'm giving you my own opinion, because Augustin's silliness is giving me a headache, so I didn't bother to read the rest of the responses.
Prayer is 100% between God and you. The Church has prayers, such as the Prayer of the Heart, which help us in relation to Him.
Personally, I find saying "Lord Jesus Christ, Son of God, Have mercy on me, a sinner." 100x on my prayer rope to lose it's meaning after a while.
This is what I say: "Lord Jesus, forgive me, the sinner." I'll break it down:
Lord Jesus: Because, obviously, we're praying to the Lord. But there is something in the name of Jesus. When I say or hear the name "Jesus", I'm put in a prayerful and reflective state of mind. Repeating His name intensifies this during prayer. I've also read that there is nothing the demons fear more than the name of our Lord.
Forgive me: Because, personally, "have mercy on me" looses meaning with me after a bit. If I have sins in mind, I don't just say "have mercy", I ask for forgiveness. I understand that both phrases could mean the same thing, but for me it's easier to contemplate while asking for forgiveness. I guess this boils down to me being more comfortable with the way the words feel in my mouth. It's like wearing comfy shoes at liturgy, it's just better overall...
The sinner: This is not so much a variation of the original, but I say the sinner, because I am the sinner. When I say "a sinner...", it makes me feel like I'm numbering myself among everyone else as a sinner. I am praying because I have sins I need forgiveness and compassion with. If I identify myself only in this way, I feel like I'm going to the police and turning myself in or something. I sin, me me me. It is easier for me to pray in this way.