How do you say that someone is a great brother for his sister ?

I noticed there's a "How do you say" thread so I decided to post the same question here as well.

How would you go about saying something like :

You're the best brother in the universe.
You're an amazing brother.

Google translate comes up with this but I don't want to sound like a translation bot and I want to make it sound rly casual and not too formal ^_^ :

Ты лучший брат во вселенной.
Ты удивительный брат.

Thanks !

Ты лучший брат во вселенной -> Ты лучший брат в мире. 'universe' is not casual word, so use 'world' instead.
Ты удивительный брат -> Ты замечательный брат. 'Удивительный' has shift in meaning to 'surprising' and probably you must use word 'замечательный' (great/remarkable/wonderful).