seperate mobile site or responsive design?

it's important to have a responsive website, and that surely affects your SEO . it will increase the bounce rate and have a negative effect on the rank of your website (because the visiteurs they will leave immediatly your website )

Responsive design definitely, easier to maintain. You can also add AMP for mobile users with slow connections.

RESPONSIVE DESIGN are perfect for mobile and desktp, now all webstes born with responsive theme.