It may depend on your health, budget, or how you upkeep maintenance. On the one hand, bags can help a vacuum last longer by keeping debris out of hard-to-clean parts that will slowly clog the machine over time. However, they will need to be replaced several times a year, and in case you have pets, they'll tend to fill up faster, and the costs can add up. On the other hand, bagless models have filters that may be costlier than bags, but it is a one-time thing, so it is a good investment. Moreover, bags are better for people with allergies or asthma because they're easier to throw out without releasing dust in the air. This is not true in the case of cleaning of filters.