There is no prayer that is “best”, but any prayer is good that turns your heart towards God and helps you express what you mean. Even (and maybe especially) those times when you just open your heart and talk to him like a loving friend.
Here are some short prayers that I have found helpful:
O Saviour of the world, by your Cross and Precious Blood you have redeemed us:
Save us and help us, I beseech you O Lord.
The Trisagion [say this three times]:
Holy God, Holy and Mighty, Holy and Immortal, have mercy on us.
Sometimes I personalize the first part of the Gloria:
I give glory to you, Father, …to you, Jesus, …to you, O Holy Spirit … As it was in the beginning [etc]
The psalms are a great source of short prayers and expressions of praise.
- Bless the Lord, O my soul! Let all that is within me praise his holy name!
- Create in me a pure heart, O God, and renew a steadfast spirit within me.
- Give thanks to the Lord, for he is good; his love endures forever.
Good hymns and spiritual songs are also good to have in your memory, especially psalms and other scripture texts set to music.
It is so lovely that God is drawing you closer to himself by giving you a desire to pray.