The connection speeds will differ via wired and wireless connections. When connected via Wi-Fi, the signal would usually have interference from other signals in your environment, which serves to slow the overall connection quality and speed. Another factor contributing to speeds is moving from one place to another in at your location. This can be reduced by placing your router in an optimum position.
Lastly, the connection and therefore speeds received from an Ethernet cable are consistent. When your PC is connected directly to the router via a cable, you will notice much improvement related to the internet connection quality and speed. To ensure you are receiving your full bandwidth, it is recommended to use the internet service via a direct LAN (wired) connection if possible. Using either option depends on your personal preference.