There are many good paid tools you can try which have free trials like SolarWinds Network Performance Monitor (NPM) and Paessler PRTG Network Monitor. The results these tools give are worth the money paid.
As you are a small company and want a free tool, SpiceWork will go better with you.
The dashboard features real-time performance graphs for all the devices on the network, which makes the screen look a little crammed. However, if there's something wrong on the network, you'll spot it straight away.
The Spiceworks network has a learning center and community forums that can help you pick up tips on getting the most out of your network monitoring software.