Installing a plugin is always a compromise. They can slow your site down. They can represent a security risk. They can conflict with other plugins or theme features.
But they can add a lot to the site user experience, or the site owner experience.
In other words, before installing a plugin, do as much research as you can about it, and potential competitors or complications.
I’ve use a lot, but not all, of these plugins over the years.
SECURITY
- WordFence
- Sucurri
SEO
- WordPress SEO by Yoast
- All in One SEO Pack
BACKUP
- Duplicator Pro
- Updraft Plus
- Backup Buddy
FORMS
- ContactForm 7
- Ninja Forms
- WPForms
TWO-Factor Authentication
- Clef
- Duo
- Google Authenticator
SEARCH
- Relevanssi
SUBSCRIPTION MANAGEMENT
- OptinMonster
CACHING
- W3 Total Cache
- WP Super Cache
EDITORIAL WORKFLOW
- Edit Flow
SLIDESHOW
- Soliloquy
GALLERY
- Envira Gallery
- NextGEN Gallery
IMAGES
- Smush
- Regenerate Thumbnails
MAINTENANCE MODE
- Coming Soon Page & Maintenance Mode by SeedProd
SOCIAL
- Floating Social Bar
- JetPack
COMMENTING
- Akismet
- Disquus
RELATED POSTS
- YARPP
- JetPack
ANALYTICS
- Google Analytics
- JetPack
CUSTOM FIELDS
- Advanced Custom Fields
EDITOR
- Tiny MCE Advanced
DATA Management
- Duplicate Post
Some Plugin-Related Links:
https://www.youtube.com/watch?v=jn3O4wOlF3Q
37 Plugins Rundown from WPMUDEV