Consider getting a theme from a well-respected company with a responsive theme. Free themes can be fun but since they are free, they can lack staying power on the market, may even have security flaws that are not considered critical to fix, and you’ll likely be wishing for ‘just a little more’ or ‘if only this did that’ functionality.
If you go for something like the Divi theme by Elegant Themes, you can find a lot of beautifully done responsive child themes for them. Divi has a lot of template packs already created by Elegant Themes that are included with membership. I have found myself wanting a better post format page, however, even now.
Also, consider the Genesis Framework by StudioPress, then for a reasonable initial investment and the purchase of a child theme, you can have something very extensible and beautiful.
However, some of these themes may be a bit slow on the loading side. Be sure to consider performance when considering what theme to purchase. Some themes are built on being optimized as much as possible yet offer a decent design.
Choosing something other than the free themes gets you much more flexibility and can help you avoid the time-suck of having to change over at a later time and then tweak everything.