Mobile design vs Mobile application

When I was just starting to create my own websites I have made lots of mistakes as a newbi. One and possibly biggest of them was not considering mobile users when creating design. So, in the end I had trouble with such users as they always bounced back from my website.

In the end, I have learned from my error and started considering mobile design during development. Nevertheless, right now I can't figure out should I consider mobile design during development or just create a mobile app for the website. Or maybe both.

What do you think?
As others suggested responsive design is the better solution. If you go for a mobile app, then you will have to design stuff from scratch or use other software or applications like tapatalk or forumrunner or something else.
You could get responsive designs for almost everything these days.
Be it a blog or forum or a website, you could get premium themes that support responsive design.
So, go for it rather than a mobile app.