I'm not a complete beginner, nor am I a total expert. Which Linux distro will go better than Ubuntu? I want one with which I can handle complex IoT easily and also browse the net and play games and chill. It must have a fairly good and intuitive GUI and it must also include all basic tools that a regular usage windows PC has.
You want the impossible! The Pi just didn’t have the same processing power as a PC.
IoT and Desktop have different requirements, although the Pi will do either.
The only Ubuntu currently available 16.04 isn’t supported on the 3+, 18.04 is still beta.
Raspbian is the official OS and works well using a basic window manager suitable for the CPU.
The GUI is not integral to the distro (as it is in Microsoft's Windows, and often presented). You just have to install a new one.
Therefore just install Raspbian, then choose a desktop GUI. You can also install Docker to help with services.
If you want a good fast desktop, and still have Microsoft's Windows or MacOs, on your desktop/laptop, then you can install Virtual-box, and put Debian on it.