Really agree with the hiding gadget angle. I don't like to see heaters, siphon tubes or even airstones.A sump can easily be set up in such a way that you can clean or replace the first mechanical filtration medium in a few seconds. You can literally remove a huge amount of waste every day if you want to, before it has a chance to be broken down by bacteria and eventually end up as nitrate in your water.
A canister filter, no matter how well designed, is much more of a PITA to clean. It takes longer to do and is pretty sloppy by comparison. Combine that with the fact that all that detritus is being collected out of sight inside the sealed canister, and the upshot is that you will be doing it far less often. Some canister manufacturers and many canister owners brag about how long you can go without cleaning...weeks or months. Think about that: you feed your fish, it poops, and that stuff gets "swept under the rug", so to speak, and sits in the water with the fish for weeks or months along with all the ensuing stuff that the fish produces during that time.
Of course, you can mitigate this a bit by vacuuming your substrate regularly. This is a great idea, especially when your canister filter is working furiously to hide all that gunk away where you can't see it. If you can vacuum it up before the filter gets it, that's a good thing. The problem is...you've gotta do it. More time, more effort. By comparison, with a sump you can use the pump outflow and perhaps combine it with strategically placed circulation pumps or powerheads to sweep bottom gunk towards the overflow, so that it gets into the pre-filter medium and you can get it out quickly. The bottom stays clean, much less vacuuming required.
If you get a bit fed up with cleaning your canister filter, take heart; cleaning your internal filter will be even more of a dog-and-pony show, so the canister won't seem so bad then.
Let's say the unthinkable happens: your pump fails. With a sump, you can easily change it, or upgrade it if you need more flow, or add a second one for redundancy. With a canister...you can buy a new canister; it'll likely cost less than buying the replacement parts you need for the old one.
Does your tank need a heater(s)? Do you see yourself adding other gadgets later, like UV or fluid media or a "Biocenosis Clarification Basket"or perhaps keeping an extra sponge filter on hand for immediate use in another tank? All of that stuff can be housed in your sump. You don't need to display the gadgets in your tank and pretend that they are "decor".
Sumps have basically only two downsides: they take up more space than other filters, usually hidden under the tank...and they might be a bit more trouble to initially set up. Once done, they make fishkeeping so much easier, save you so much time and have so many advantages that I personally think you would be doing yourself a huge disservice by not using one.
Like the tank to look as natural as possible. Like a slow moving river. Open air sumps also help with tank aeration.
