These threads are funny. Everyone just spouts off their favorite model and brand.
How about we try to reduce the list down a bit with these questions.
What is your budget?
What type of stocking do you have?
Is it planted or non-planted?
How important is noise to you?
How often difficult of setup do you want to do?
HOB's (hang on the back) filters are generally cheaper, louder, easy to setup, and easier maintenance. They also have limited configurations and smaller media space available. They are also not good for planted tanks if you are running CO2.
Canisters are the quietest, more difficult to setup and maintain, more expensive, and contain more media space. They have many different configurations and large media baskets.
Wet-Dry. Has the most media space, is expensive to setup, but has very little maintenance requirements. They can also be the most difficult to setup and require the most space under the tank. You also sometimes get the sound of running water with them and some motor noise.
BTW I run a Magnum 350 and C-360 on my 125. The combo works great.