Ron

Harry says Ron is but Hermione is the one that never left his side even when things got realy tough

The one who stuck by him through everything.

Hermione, of course

He was Harry first friend. That kind of bond sticks with you and strengthens your relationship.

both

Ron left Harry twice, when he needed the most

I love their sister/brother relationship. That's why they never felt weird in each other's company. She had always been there for him, especially in rough times.

Hermione stood by Harry in his toughest times

Hermione made her parents forget who she is just to help Harry with his journey to find the Horcruxes, Ron left Harry for more than one time

both

Ron left Harry two times when He needed Him, also Hermione was kind of more helpful.

Hermione stuck with him till the last moment