Good beginner-intermediate snake?

[SupaSnake]

Hey there I am sure you guys get these sort of posts all the time, But I am really interested in buying a snake... My brother had 2 Ball pythons and he currently has a (Im not sure what it is but Im sure its) Jungle carpet python

I dont neccisarily want a ball python because I think they're a little fat... I want a constrictor though, I couldnt decide between a Python or Boa so I was wondering if anybody could help me out with some useful tips for any cool snakes that arent really common that arent too hard to handle

Any help would be greatly appreciated!