Filter systems can be purely a matter of personal prefernce. I have for many years favoured the use small box filters in all my smaller breeding tanks. They are generally cheep to buy and easy to maintain. More recently though I have taken to using a wider range of sponge filters to replace the box filters.
Box filters work very well in the smaller breeding tanks and easily maintained, they can also be filled with moss peat or other water conditioning agents.
The "Poly filter" has been a favourite of mine for many years and are used in small fry rearing tanks.
Most of these are either 10 cm square by 5 cm deep or 10cm cubes and have a weighted base to help them hold position on the bottom of the tank. There are many adaptations to the basic system, which is to draw water at a steady rate through a piece of sponge to remove suspended particles, fish waste. It takes a little time for a new filter to mature and become colonised by nitrifying bacteria, but once mature are very efficient.
For the larger stock tanks I used to favor outside canister filters, although each tank now (December 2012) has full width "Matten" filters.
Canister filters come in all shapes and sizes, with varying flow rates, again these are all a matter of choice. I prefer the Eheim Ecco range, of which there are three basic sizes, a two, three and a four chambers. One of the reasons I like these filters as well as there efficiency and reliability, is because they are equipped with a handle, making it easy to hang them near to where they are needed. All the filter inlet pipes are situated behind the "Matten" filter sponges, so the actual flow rat is increased.