Filters are essential to the cleanliness and overall health of your aquarium. There are several types of filters, which are explained by Redditor /u/AsusMeMoPadHD7 below:
Pros: Often completely silent, no need for additional space behind or under the tank.
Cons: Messy maintenance, as the complete filter will have to be removed and disassembled.
Pros: Very large, very easy to overfilter and thus keep your parameters stable. Requires rather infrequent maintenance.
Cons: Large, requires some space under / near the tank, and some cheap models are loud.
HOB (Hang On Back)
Pros: Usually rather quiet, very easy maintenance (the filter cartridge can often be removed separately from the pump and casing).
Cons: Requires room behind the tank, intake on smaller models can be prone to clogging.
Additionally, all non-internal filters have a (very, very small) risk of leaking or spilling, either during maintenance or as the result of a malfunction.