Two Kids and a Coupon on MSN: 6 free thank you coloring pages
Tell those you love how much you appreciate everything that they do with these free thank you coloring pages for kids and adults.
The base meaning of "they are the best of friends" is more something like "of all the friendships you might encounter in the world, theirs counts among the truest/closest". In other words, here "of friends" means "of all the various friendship relationships". So, it's just saying the people in question are very good friends, but it's a distinctive phrase that's often used to emphasize that ...