2060, 1070ti and 1080 are very near to each other.
Assuming the card is new, I would grab the cheapest.
If you ask me between a second-handed 2060 or 1080, 2060 is my pick.
You can never know how the previous owner used the card, heavy 24/7 mining? etc. etc.
I would not be that worried if it is only about the VRAM capacity. Just pay attention with 2060 you are looking at.
If I understood it correctly 2060 should come in several variants. The one on par with 1080 is the highest variant of 2060.