There are best wordpress plugins all time and they are used have millions of downloads.

1.Yoast SEO

Yoast SEO does everything in its power to please both visitors and search engine spiders. How? Below you’ll find a small sampling of the powers of Yoast SEO:

• The most advanced XML Sitemaps functionality at the push of a button.
• Full control over site breadcrumbs: add a piece of code and you’re good to go.
• Set canonical URLs to avoid duplicate content. Never have to worry about Google penalties again.
• Title and meta description templating for better branding and consistent snippets in the search results.

2.Maintenance Mode

You are make many new post or update a websites so you create a simple Coming Soon Page or Maintenance Mode Page. Work on your site in private while visitors see a “Coming Soon” or “Maintenance Mode” page.

• Works with any WordPress Theme.
• Responsive.
• Customize the Look and Feel.
• Easily add Custom CSS and HTML.
• Uses HTML5 & CSS3.
• Uses WordPress Best Practices.

3.Jetpack

Jetpack is your site’s security detail, guarding you against brute-force attacks and unauthorized logins. Basic protection is always free, while premium plans add expanded backup and automated fixes.

• Brute-force attack protection, spam filtering, and downtime monitoring.
• Backups of your entire site, either once daily or in real time.
• Secure login, with optional two-factor authentication.
• Malware scanning, code scanning, and automated threat resolution.
• A record of every change on your site to simplify troubleshooting.

4.Really simple SSL

This Plug is used Really Simple SSL automatically detects your settings and configures your website to run over https.

• Activate this plugin.
• Enable SSL with one click.

5.Social Media

This Plug is very usefull for Social media share's.Let’s you add share icons for RSS, Email, Facebook, Twitter, LinkedIn, Google+, Pinterest, Instagram, Youtube, ‘Share’ (covering 200+ other social media platforms) and upload custom share icons of your choice.

• Pick from 16 different designs for your social media share icons.
• Select from many other customization features for your socialmedia icons!.
• Decide to display sharing-buttons and social media icons at the end of every post.
• Allow visitors to subscribe to your blog by Email.

6.Migrations

This Plug is used for copy, move or clone a site from one location to another and also serves as a simple backup utility.

• Move, migrate or clone a WordPress site between domains or hosts with zero downtime.
• Pull down a live site to localhost for development.
• Transfer a WordPress site from one host to another.
• Manually backup a WordPress site or parts of a site.

7.Mega Menu

Max Mega Menu will automatically convert your existing menu or menus into a mega menu. You can then add any WordPress widget to your menu, restyle your menu using the theme editor and change the menu behaviour using the built in settings.

• Builds upon the standard WordPress menus system.
• Supports multiple menu locations each with their own configuration.
• Drag and Drop Mega Menu builder.
• Menu item options including Hide Text, Disable Link, Hide on Mobile etc.

8.Akismet

Akismet checks your comments and contact form submissions against our global database of spam to prevent your site from publishing malicious content.

• Automatically checks all comments and filters out the ones that look like spam.
• URLs are shown in the comment body to reveal hidden or misleading links.
• Moderators can see the number of approved comments for each user.
• A discard feature that outright blocks the worst spam, saving you disk space and speeding up your site.

9.Google XML Sitemaps

Use this plugin to greatly improve SEO to create special XML sitemaps which will help search engines like Google, Bing, Yahoo and Ask.com to better index your site.

10.Contact form 7

Contact Form 7 can manage multiple contact forms, plus you can customize the form and the mail contents flexibly with simple markup. The form supports Ajax-powered submitting, CAPTCHA, Akismet spam filtering and so on.

11.Wordfence Security

THE MOST POPULAR WORDPRESS FIREWALL & SECURITY SCANNER.Wordfence includes an endpoint firewall and malware scanner that were built from the ground up to protect WordPress

• Web Application Firewall identifies and blocks malicious traffic. Built and maintained by a large team focused 100% on WordPress security.
• [Premium] Real-time firewall rule and malware signature updates via the Threat Defense Feed (free version is delayed by 30 days).
• Protection from brute force attacks by limiting login attempts, enforcing strong passwords and other login security measures.

12.Regenerate Thumbnails

Regenerate Thumbnails allows you to regenerate all thumbnail sizes for one or more images that have been uploaded to your Media Library.

• A new thumbnail size has been added and you want past uploads to have a thumbnail in that size.
• You’ve changed the dimensions of an existing thumbnail size, for example via Settings Media.
• You’ve switched to a new WordPress theme that uses featured images of a different size.

13.WP Super Cache

This plugin generates static html files from your dynamic WordPress blog.

• Users who are not logged in.
• Users who have not left a comment on your blog.
• Or users who have not viewed a password protected post.

14.Google analytics by yoast.

Google Analytics Plugin for WordPress:We believe that it’s easy to double your traffic and sales when you know exactly how people find and use your website. MonsterInsights shows you the stats that matter, so you can grow your business with confidence.