I prefer canisters myself, but it's all personal choice more than anything. On one of my tanks I have a XP3 and XP4 canister, then on the other I have an xp3, and on the new 265g tank I will be getting shortly I plan to have probably two FX5's.
For me canisters are just simply much easier. I have never built a sump, and with the canisters now a days they hold a huge amount of media. I have around 2-3liters of media in each of my canisters and could probably pack even more in if I wanted, and in an FX5 you can get even more media in those than my Renas have. So I don't see a need to have more media than you really need. My heaters are all Hydor inline heater so they mount on the canister and are out of the tank. And I like the fact that the canisters take up less room under the tank than a big bulky sump does.
But like I said I really think it is just a matter of what each person likes. They both have good and bad to them just depending on what you consider good/bad.