Longer is better, because you can always cut excess. You can't add any to a short one.
I daisy chain the short ones together, male to female ends, to make long ones out of short ones. Clunky, but effective, especially because I fell for one of those package deals which gives you a thousand zip ties, broken down into 100 eight inch and 900 three inch. I saw some 48 inch zip ties at wally world recently,