I am assuming it is not drilled for a sump or wet/dry, right? If not, your hood will tell you what is best. If it is already cut for a HOB filter, then that is your best bet. Stick with something with a bio-wheel such as a Penguin. I have a hex that I put a sponge filter in just for simplicity. I wanted to drill the tank but the space inside the stand is too small for a filter (I don't like canisters).
Much of it depends on the type of fish you plan on keeping. Hex tanks have less surface area per gallon than most tanks being taller tanks, so have to be stocked on the light end. Being deeper means you want to have some circulation on the bottom. The type of fish will determine the best filtration, and how to accomplish better circulation with that particular filter.