Usually I do each stage the same number of time (like 10~20 each) to get as much stuff as possible. Use all your stamina potion on it if you want. It's almost the best way to use them (to other good stages to use them is Nidhogg phase 2 stages but at low level is near to impossible to get enough currency to clear the shop. But don't worry, shop refill just stack and you will be able to get everything some days).

If you have a lot of stamina potions, it's better to do secret gardens as they give Manyu and Life Crystals. If you need stamina free XP to level up, you can do Manyu Key stages for quicker level up and stamina refill.