This is your preference, either are accepted. However, any liner bag used MUST BE certified compostable, from BPI. (BPI=Biodegradable Products Institute)
Note, product labels can be misleading. Those bags labeled "biodegradable" or "environmentally friendly", etc. without the BPI certification ARE NOT ALLOWED.
These will not break down fast enough to compost and will cause an entire cart to be landfilled. Please beware of misleading products.