I really cannot offer much advice at all on WP themes. I just don’t have experience with many themes. I find one that works well for me and stick with it. I want a theme that provides a framework and does not get in my way. Also – a personal preference – I want users to immediately see content, not a ginormous image that takes up the entire landing page above the scroll. Initially I used Twenty Ten, which I liked quite a bit, but eventually it became obvious that a modern website must be responsive. I switched to Responsive Mobile from CyberChimps, and have used it ever since. It meets my needs and offers a simple but powerful set of Theme Options that make it easy for me to add custom CSS styles and header/footer scripts. It seems lean. A comparison of file sizes to the current default theme:
With the huge number of high quality free themes available in the official WP themes directory, I see no reason to consider themes from other sources, including ‘Pro’, ‘Premium’ or otherwise ‘Pay’ themes. If I were to try a theme from a source other than the official WP directory, I would want to be very, very sure it is a reliable source. How to be sure? I have no idea, I only consider free themes from the official WP directory.
For most WP users, the current default theme – Twenty Seventeen at the time of this post – seems a good place to start.