Get something 30C, or higher. I ran 20C for ages but they struggle if you use too much WOT. And you don't need high power and cost, of say over 40C to 65C sort of things. Unless you do have some other reason to have those (eg some higher power 5S 70mm combo). But if you do go higher C, it will raise the power level, and Amps, thus less flight time if you use it, plus the ability to overstress the motor then.
Zippy/ Zippy Compact have some very good value batteries (30C or 35C) that will cope fine.
eg Zippy Compact 5S 3300mAH or 3700mAH in 35C
It will carry either of these fine:
I have/use from 5S 3000 30C, 3300 35C, 3700 35C, 4000 40C
(used to use mainly 5S 3000mAH 20C)