What I have known is that too many plugins will affect load speed a lot. So few is the best. I have couple of sites and I use following. 1. Yoast SEO free version (More than enough) 2. Simple Social Icons (Social media sharing) 3. Wp Super Cashe (Free and simplicity) 4. Akismet (Anti-Spam) 5. Contact Form 7 6. Vaultpress (Security) I'm more than happy with these plugins. Please note, my sites are blogs. Not ecommerce site.