There is no best. Only least worst. Pick your poison:

AMD: Libre driver stack, require firmware blobs.
NVidia: Proprietary driver stack (kernel driver component slowly being opened), proprietary firmware exists in ROM on card so doesn't need to be loaded at runtime.
Intel: Libre driver stack, same firmware issue as with NVidia, GPU performance generally sucks because iGPU constraints

I would say, in order from least-worst to most-worst:
AMD
Intel
NVidia

Others that I have considered, but are hopeless pipe dreams
Matrox - old, deprecated, dead, no longer in business?
S3 Chrome - assimilated into Centaur/VIA technologies, later bought out by Intel
Mali - don't even kid yourself
Software rendering - you must be desperate
Aspeed and other 2D framebuffer solutions - good luck
Any and every "open source GPU" initiative - always dead in the water. NLnet recently pulled funding from LibreSOC because the lead dev spent more time begging for e-gold than doing any developmental work.