There are quite a few premium themes on the market that come in with a lot of features, but what should you choose?
If you're planning to build a bit more serious website and don't have the time / money / skills to build your own custom theme, buying a premium theme is a good option.
If you're planning on buying some premium plugins for your project, it is also worth checking if that plugin/plugins is packaged into some premium theme. This way, you might even end up saving some money.
Don't go randomly looking for different themes and just pick something that looks nice. Design can be easily changed and a nice screenshot or a demo page does not tell whether the theme is good for your project. Start first thinking what you need for your project, before going window shopping. Maybe go old school, grab your legal pad and do a list of the must haves.
There is a neat little trick, that allows you to view a lot of demo websites using a specific Wordpress theme. Google "wp-content/themes/themename" to view different pages that use the theme, by replacing the thename with the theme name that you want to view samples from.
I've used a premium theme called Kalium a few times at work, and can highly recommend it. It costs USD $59 as we speak at Theme Forest, and comes with rich features and good plugins, like Visual Composer and Revolution Slider. Those two plugins would already cost you close to the theme's price, if you would buy them individually. Of course, the plugins that come bundled with themes usually lack some possibilities for the end user, that you would get when just buying the plugin. For example, support is usually one of these features that you might be lacking with the bundled plugins.
Plugins that come with Kalium:
Besides quality, Kalium has gotten awards and mentions for its design as well. There are quite a few awards and mentions that the theme has received in multiple medias, including the honorable mention from AWWWARDS in 2015.
Kalium has been already translated into multiple languages, and supports WPML, the multilingual Wordpress plugin straight out of the box. It also supports WooCommerce. It is rich in features without being overwhelming.