I'd say Blocky. I'm better friends with him.
Blocky smiling
207px-Snowball 5

This page is about the chemistry between Snowball and Blocky. The two seem to be very good friends with each other, as they are both known to be bullies.

Episodes suggesting a friendship

In Take the Plunge: Part 1, Snowball and Blocky are seen talking to each other, along with Pen and Eraser.

In Take the Plunge: Part 2, Snowball talks to Coiny and Blocky about how Flower is getting on his nerves.

In Insectophobe's Nightmare, Snowball chooses Blocky over Firey when choosing the teams, saying that he's better friends with him.

In Crybaby, Snowball high fives Blocky because he is safe with 2 votes.

In Half a Loaf Is Better Than None, Blocky, along with Eraser and Pen, cheer for Snowball.

In Return of the Hang Glider, Snowball is seen with Blocky when Firey is deciding who should go on this island and who should not.

In Yeah, Who? I Wanna Know, Snowball is briefly seen in the beginning with Blocky, as well as Eraser and Pen, when Pen says "Hey, guys, look!" and points at TV.

Episodes suggesting a conflict

In Lofty, Blocky pops Snowball's balloon.

In A Leg Up in the Race, Blocky seems happy when Snowball gets extracted by 18 points. This could be, however, just Blocky's regular state.