Category page vs page with blogposts from category

Hi,

My site is almost ready for launching.
But i need to decide to use the standard category page (for posts) or make a new page for each category.

I have 5 categories and i need to link to them in the menu.

I really like the masonry layout and i think i can only implement this when creating a page for each category and put the masonry layout in it.
But my question is:

Does this not create a SEO problem.
Because i would have mysite.com/news (masonry page) AND mysite.com/blog-news (category page).
So that would be duplicate content.
And im afraid maybe the category page would be indexed higher then my own created page.

What to do?