1st PC

PCO (Perfect Clear Opener) is the most common perfect clear opener. It has a 84.64% chance to PC which drops to 61.19% when the I block is placed.

four.lol has a good guide on this. There is also a website to practice all PCO solutions.

Grace System is a perfect clear opener that places the J, L, S, Z, O, and I pieces in a 6 by 4 rectangle. It has a 88.57% to PC. When the T block is placed, it becomes identical to PCO.

four.lol has a good guide on this.

A perfect clear opener that places the I, S, Z, and J/L pieces. It has a 100% chance to PC, making it the only perfect clear opener that uses 4 or more pieces and still has a 100% chance to PC. It isn't useful for VS games due to how difficult it is to see solutions.

four.lol has a good guide on this.

4 piece setups with the highest chance to PC. Some of these are impractical due to how difficult it is to find solutions.

Every 3 piece setup that has a 100% chance to PC. 6 out of 18 are just 3 ILSZ placements. Note that these are only 100% with 6 previews, which most games don't give you. However, they are still good for freestyling 1st.