I have two ways of writing dialogue.

(1st way)

> 
> Issac said in an angry tone, "I don't care what you want! Just leave me alone!" However, I comforted him and said, "All I care for is you. I can't leave you here alone! Never!"
> 
> 
> 

(2nd way)

> 
> Issac: I don't care what you want! Just leave me alone!
> 
> 
> Me: All I care for is you. I can't leave you here alone! Never!
> 
> 
> 

I usually prefer the second one as it's neater. However, my teacher prefers the first one because it's more grammatically correct. So, which way should I choose for my further writing and why?