Performance is not a precise thing, so I'll try to differentiate: The best experience is GPU passthrough, so that you have the full power of your GPU at your fingertips. SPICE is the second best option to have a working VDI-like infrastructure because it'll passthrough your clipboard, you have dynamic window resizing, audio passthrough and decend graphics performance due to graphics offloading to the client. This technique is similar to RDP, yet lives at the virtual hardware level and not on the OS level. The default VNC is fine for "just doing some GUI stuff" like configuring a server. You won't have clipboard sharing or audio passthrough and everything is done on the client and uploaded to your browser.