PCI passthrough currently seems to be the most popular method for optimal performance. PCI GPU passthrough PCI VGA/GPU passthrough via OVMF
However, it is not designed to offer near-bare metal performance. QXL/SPICE is a high-performance display method. Methods for QEMU guest graphics acceleration QXL video driver and SPICE client for display 1.4 Virgil3d virtio-gpu paravirtualized device driver.1.3 Fully virtualized GPU support via Intel-specific iGVT-g extension.1.1 QXL video driver and SPICE client for display.1 Methods for QEMU guest graphics acceleration.