It's a bit difficult to recommend some specific tools. Primarily because "the best" and "most easy-to-use" aren't always synonymous. Are you looking for certain features or a specific category of tool? 

Some things to keep in mind. Productivity tools is a pretty broad category that usually consists of the following types of software:

1. Project management software - Classics such as Gantt charts, Kanban boards with a modern twist. Trello and Wrike are the big names here. 
2. Time tracking apps - Devices which measure how long you spend on certain tasks. Time Doctor and Toggl are common.
3. Collaboration tools - Digital workspaces such as Slack or more specialized platforms where you can work together as a team on documents, such as Proofhub or Google Docs.
4. Scheduling software - Task, calendar and resource scheduling. My company Ganttic is more resource specific, but others include Calendly, Todoist, and even Excel.

Most likely you'll need a combination of at least some of these to be the most productive. We had a really great guest post on our blog by a small business owner, Ayomide Joseph, where he lists specific use cases of his top 10 favorite free business tools: https://www.ganttic.com/blog/10-free-business-tools-for-startups
It breaks down these categories and offers some nice insight for other business owners.

Also be on the lookout for specific features. Because certain things can make or break the way you use these tools. Here’s a few software features that increase productivity:

Shareability - Depends on the tool, but you should think about who needs access. Is this mostly for management? Or are you creating something that needs to be shared with your team? Or even amongst outside entities, such as clients or freelancers? Whoever needs access, the issue then often comes back to price.

Use - How is it deployed? And how long will set-up take? Cloud-based is probably your best bet. It’s quick, easy, and can be accessed from anywhere. Especially since remote work won't be going away anytime soon. And even when we do return to the workplace, it's likely there will be many who implement a more hybrid approach with some people working remotely while others remain in the office. So not only do you need something that can be accessed remotely, but you also need to consider how it can help with the management of new ways of working.

Integration - Because you (probably) won’t be using just one piece of software, it’s better to connect your tools together. Not only does this cut down on the time of manually transferring and reproducing data, but it cuts down on human error. Many tools come with native integrations, but also keep in mind aspects such as APIs or Zapier accessibility. That way, as you grow as a business, you’ll have the option to sync your new tools down the line. 

At the end of the day, the best productivity tools boils down to your individual needs. More expensive isn’t always better, but it’s also not the best idea to cut corners on something that you need everyday.