If you're going for a canister you'll want an inline heater to keep the tank looking 'clean', not worth the hassle IMO, sump is the best option.
If you're building the whole thing from scratch set it up with a "coast to coast" style overflow at one end that will be hidden by the wall (and will also be near silent if set up with multiple "bean animal" style drains) and plumb the return through the overflow to minimise the amount of visible equipment in the tank. This is exactly how the overflow on my old 400L reef was set up, and would be ideal for an in-wall or peninsula type set up with both sides visible.
There were four holes in the base of the overflow, one drain controlled with a ball valve running at full siphon [silent], another drain with durso taking the ~5% of flow not taken by the full siphon [silent], another drain as a back up in case either of the other two got blocked, and the fourth hole had the return coming back up from the sump.
Obviously if you already have the tank or are planning on buying used then it isn't a feasible option, but if you're going new and want both sides clear for viewing then IMO you won't find a better set up.