2060 if it's the 8 GB version, otherwise 1080. But obviously the best would be to not waste your money and just buy cloud compute... With these cards being 200-300$, that is roughly 200-300 hours of A100 training, which is much faster and enables you to train much larger models.

EDIT: I see you've gotten a 110$ offer for 1080, I'd say go with that. You'll be severely limited in what you can run but after you learn your lesson you can still sell it for 100$, or even more.