I've noticed that in my Home-WiFi there are some WiFi-Clients that have an incredibly slow internet connection (less than 2-3Mbps), while wired and newer WiFi devices can reach close to their full Network speed of 100Mbps. For Example, my Roku Express HD Streaming Devices had very long buffering times, while being 2 meters away from the home TP-Link router. It almost felt like my router preferred some devices, while others had almost no bandwidth, even when no other device was used in the WiFi-Network.

Solution:

- Go to your TP-Link Router Interface at 192.168.0.1 and navigate to "Wireless" > "Wireless Settings"
- Select Mode : set 11gn mixed or 11n. It is important that 11b isn't selected, as it is now an outdated and slow standard that some devices fall back to.
- Save settings

If this isn't enough, you can use a tool like "WiFi-Analyzer" that shows the 2.4GHz WiFi-channel usage of nearby routers, so that you can select an empty channel number in the previous "Wireless Settings", don't forget to save.