This is my list of my favourite plugins, that will ensure good performance and security or other functions.
It might change from project to project time to time, but in average these are the plugins I use most likely.
Genesis eNews extended
It allows embedding newsletter subscription form into your website easily.
You can add contact form or any other form to your website.
Simple social icons
This one is for simply adding social media icon to your website.
Optimizes your images. This is very good for page speed.
The best SEO plugin.
Wordfence is a robust and complete security system for WordPress. It protects your WordPress site from security threats and keeps you off Google’s SEO black-list by providing a firewall, brute force protection, continuous scanning and many other security enhancements.
Wordfence also detects if there are any security problems on your site or if there has been an intrusion and will alert you via email. Wordfence can also help repair hacked sites, even if you don’t have a backup of your site.
Best backup plugin out there. Backup can save your website if something happens and you need to restore it.