assuming mainstream video card (~560Ti or less / ~7790 or less), order of priority:
1. DDR5 is better than DDR3, regardless of capacity.
2. 2GB is better than 1 GB.
3. 2 fans is better than 1 fan.
example:
1GB of DDR5, with 1 fan card would be better than 2GB DDR3 with 2 fans card (assuming same GPU).
2GB DDR3 with 1 fan is better than 1GB DDR3 with 2 fans.