My 5-year-old son has a 5 year old best friend.

His friend is the kind who is always telling my son, that he is better or his things are bigger and better.

His friend is always telling him:

I am taller than you
Your water bottle might be taller, but mine is wider, so can hold more water than yours.
My daddy is stronger
My shoes are better than yours

It happens a lot when us parents are around as well. An example would be:

Friend: I am taller than you
Son: <not knowing what to say>
Me: It's ok, doesn't matter who's tall or short as long as they are healthy and active.

Both of them drinking milk

Friend: I finished drinking my milk before you
Son: <not knowing what to say>
My wife: It's ok, it doens't matter who drinks their milk first, its only important to finish.

Both of them playing a game of junior monopoly:

Friend: My daddy is stronger
Son: No my daddy is strong too
Friend: No your daddy is only 30 something years old, my daddy is 42, so he is stronger.
Son: <Not knowing what to say>
This happened in school, my son asked me yesterday if his friends daddy was stronger than me and then narrated this story.

I am aware there are going to be kids like this and it's part of growing up.

But I am also thinking it isn't good for my son to have a best friend who is constantly putting him down or making him feel inadequate.

His friend isn't a mean child, but just that it is in his nature that he sees a need to be first, a winner all the time. He is also manipulative, where can convince my son into doing things he wants to do or play games that he choose to play. Yes, all this at 5 !

What should we teach our child? What should be the right thing to say on his own without feeling inadequate? or being a mean to put his friend down?

There are many things my son does better, like he can read, when his friend cannot read at all yet. My son is good with his number and can count to a 100, when his friend hasn't yet caught up with his counting.

We don't want him to start doing the same thing and learning to say that he is better, at the same time we don't want him to keep listening to this and just think he isn't good enough?

Any advice, suggestions welcome.