I have a lot of experience flipping.
Theres no one size fits all for this. Youve got to take a look at the specific numbers and decide what currencies are good to flip. The key is the balance between margins and flip rates.
Its usually better to flip for ratios slightly lower than the maximum you can theoretically get (while still turning a profit) to encourage quicker sells. Generally making 1 sale while squeezing out every last bit of value is worse than making multiple sales at smaller profit but which overall net a higher total. If you have to be greedy, be greedy when youre a buyer and easy going when youre a seller. Rinse repeat and snowball your wealth, don't spend your currency too early.