Depends on your comfort level. If you have $10 unit size with a $1,000 bankroll, but will lose your mind if you lose $500 (50 units), then its better to have a $5 unit size with $1,000 bankroll or .5% as your unit size. I personally like using 200 units as my bankroll size, with a $2,000 bankroll I would play $10 units. Feels pretty safe that way. Other people get greedy and if they dont double their roll they feel like they have not succeeded so will use like a $40 unit size with a $2k roll. All depends if your bankroll is replaceable.
Usually bet sizes range from 1u up to 5 or even 8 units with a downswing of around 50 units at some point in time. Labby usually makes it pretty consistent, but variance always happens.