Bagless vacuums are not better than vacuums with bags if you are looking at performance. Performance has more to do with the type of suction (funnel suction works best) than whether or not the vacuum has a bag. In fact, both types of vacuums lose suction over time, according to Consumer Reports. Still, there are benefits and disadvantages to each type of vacuum.
Bagless vacuums collect dirt and debris in a collection container. Usually, these containers are clear, so you can see how much dirt you are accumulating and when to empty them. Emptying these containers can be a messy business, especially if you jar or accidentally spill the cup. Bagless vacuums have separate filters that need to either be replaced or cleaned on a regular basis. On the plus side, bagless vacuums are usually less expensive to maintain as the collection containers seldom need to be replaced.
Vacuums with bags collect the dirt and debris in a bag. Once the bag is full, you simply remove the bag, throw it away and replace it with a new, empty bag. Many vacuum bags come with built-in filters, which helps to filter the air as you vacuum. For this reason, they are a better choice for people with allergies. On the other hand, constantly having to replace your vacuum bag can be hard on the wallet.
Most upright vacuum cleaners have bags, although some (most notably the Dyson brand vacuums) are bagless. Many people prefer uprights because they are easier to handle. In addition, upright vacuum cleaners generally clean carpets better than canister models, according to Consumer Search.
Canister vacuums do not usually have bags. People who use canister vacuums like the way they can reach underneath couches and other tough-to-clean locations. These vacuums are also easier to move from room to room and are easier to use on stairs. Canister vacuum cleaners are also usually quieter than their upright counterparts.
While determining whether or not you want a vacuum cleaner that uses bags is important, there are also other things to consider. A vacuum that uses a revolving brush should have a way to turn off the brush if you will use it on bare floors since the motion of the brush often spits back dirt when used on smooth surfaces. Consider other intangibles as well. Choose a light vacuum if you will carry it around a big house, and get one with pet hair removal attachments if you have pets that shed.