I usually prefer building WordPress websites from scratch as it allows me to give them specific functionality, layout and more importantly is so much more fun. Bespoke builds are usually less vulnerable to generic, automated attacks – those are targeted at popular plugins and themes.
But if a job needs to be out in few days (or hours), well…
In such cases I prefer to rely on WordPress.org themes, always bundled with a release of WordPress CMS system. They are well documented, easy to customise and I can be sure that they won’t contain any malicious code.
For this example, TEDx Youth @HamptonCourtHouse, I used Twentyfourteen theme with only few additional lines of code.