EmuNations

Dolphin is a GameCube and Wii emulator which supports resolutions beyond Full HD with several enhancements: compatibility with all PC controllers, turbo speed, networked multiplayer, and much more.

You have to experiment with the different graphics backends (D3D, OpenGl, Vulkan, etc.) as performance can vary significantly depending on your hardware. Please follow their guide for more details!  Rule of thumb: Start with the lowest resolution and increase while gameplay/sound aren't choppy.

For game enhancements (smoothing, anti-aliasing, etc.), apply same principle as mentioned previously while taking into consideration resolution. 

It's basically a fork of the Dolphin emulator providing support for legacy devices and other features such as reducing CPU usage on the graphic's thread.The focus seems to be more speed and less on accuracy. 

Please read extensive features via Forum page (GC/Wii section). That said, unless you're feeling quite adventurous or have very old hardware (i.e. D3D9), try the regular Dolphin first. Some people have reported this version works better for them, but it's not a general consensus.

Pureikyubu (formally Dolwin) is an open-source Nintendo GameCube emulator which initially started development in 2004. It went into hiatus but is now active. With that in mind, it's not the most advanced but has interesting features and is able to boot and run some commercial games and demos.

• Emulation requires DSP IROM / DROM dumps

• A BIOS image dump is not required, but if you want to experiment with it, you can also add it in the settings. The BIOS is launched through the menu File -> Run Bootrom. Then you need to wait a bit and open the drive cover (File -> Swap Disk -> Open Cover). After that, IPL Menu will start :p