sump for sure..... canisters are way expensive and they dont work nearly as good (especially with bio filtration. you can also have ALOT more media. you could also put in plants as a nitrate remover.
With a DIY sump you can filter thousands of gallons with one pump and some creative plumbing. They can also house heaters and other doohickeys that tend to clutter the display thank. Very efficient to operate and clean too.